diff --git a/nixos/doc/manual/release-notes/rl-2105.xml b/nixos/doc/manual/release-notes/rl-2105.xml
index c730ed4e85f..566cd5d7240 100644
--- a/nixos/doc/manual/release-notes/rl-2105.xml
+++ b/nixos/doc/manual/release-notes/rl-2105.xml
@@ -573,14 +573,16 @@ self: super:
    </listitem>
    <listitem>
     <para>
-     The default-version of <literal>nextcloud</literal> is <package>nextcloud20</package>.
+     The default-version of <literal>nextcloud</literal> is <package>nextcloud21</package>.
      Please note that it's <emphasis>not</emphasis> possible to upgrade <literal>nextcloud</literal>
      across multiple major versions! This means that it's e.g. not possible to upgrade
-     from <package>nextcloud18</package> to <package>nextcloud20</package> in a single deploy.
+     from <package>nextcloud18</package> to <package>nextcloud20</package> in a single deploy and
+     most <literal>20.09</literal> users will have to upgrade to <package>nextcloud20</package>
+     first.
     </para>
     <para>
      The package can be manually upgraded by setting <xref linkend="opt-services.nextcloud.package" />
-     to <package>nextcloud20</package>.
+     to <package>nextcloud21</package>.
     </para>
    </listitem>
    <listitem>
diff --git a/nixos/modules/services/web-apps/nextcloud.nix b/nixos/modules/services/web-apps/nextcloud.nix
index de1c67235f4..5636415f6a0 100644
--- a/nixos/modules/services/web-apps/nextcloud.nix
+++ b/nixos/modules/services/web-apps/nextcloud.nix
@@ -28,7 +28,10 @@ let
     upload_max_filesize = cfg.maxUploadSize;
     post_max_size = cfg.maxUploadSize;
     memory_limit = cfg.maxUploadSize;
-  } // cfg.phpOptions;
+  } // cfg.phpOptions
+    // optionalAttrs cfg.caching.apcu {
+      "apc.enable_cli" = "1";
+    };
 
   occ = pkgs.writeScriptBin "nextcloud-occ" ''
     #! ${pkgs.runtimeShell}
@@ -86,7 +89,7 @@ in {
     package = mkOption {
       type = types.package;
       description = "Which package to use for the Nextcloud instance.";
-      relatedPackages = [ "nextcloud18" "nextcloud19" "nextcloud20" ];
+      relatedPackages = [ "nextcloud19" "nextcloud20" "nextcloud21" ];
     };
 
     maxUploadSize = mkOption {
@@ -280,6 +283,24 @@ in {
           may be served via HTTPS.
         '';
       };
+
+      defaultPhoneRegion = mkOption {
+        default = null;
+        type = types.nullOr types.str;
+        example = "DE";
+        description = ''
+          <warning>
+           <para>This option exists since Nextcloud 21! If older versions are used,
+            this will throw an eval-error!</para>
+          </warning>
+
+          <link xlink:href="https://www.iso.org/iso-3166-country-codes.html">ISO 3611-1</link>
+          country codes for automatic phone-number detection without a country code.
+
+          With e.g. <literal>DE</literal> set, the <literal>+49</literal> can be omitted for
+          phone-numbers.
+        '';
+      };
     };
 
     caching = {
@@ -345,10 +366,13 @@ in {
             && !(acfg.adminpass != null && acfg.adminpassFile != null));
           message = "Please specify exactly one of adminpass or adminpassFile";
         }
+        { assertion = versionOlder cfg.package.version "21" -> cfg.config.defaultPhoneRegion == null;
+          message = "The `defaultPhoneRegion'-setting is only supported for Nextcloud >=21!";
+        }
       ];
 
       warnings = let
-        latest = 20;
+        latest = 21;
         upgradeWarning = major: nixos:
           ''
             A legacy Nextcloud install (from before NixOS ${nixos}) may be installed.
@@ -366,9 +390,9 @@ in {
           Using config.services.nextcloud.poolConfig is deprecated and will become unsupported in a future release.
           Please migrate your configuration to config.services.nextcloud.poolSettings.
         '')
-        ++ (optional (versionOlder cfg.package.version "18") (upgradeWarning 17 "20.03"))
         ++ (optional (versionOlder cfg.package.version "19") (upgradeWarning 18 "20.09"))
-        ++ (optional (versionOlder cfg.package.version "20") (upgradeWarning 19 "21.05"));
+        ++ (optional (versionOlder cfg.package.version "20") (upgradeWarning 19 "21.05"))
+        ++ (optional (versionOlder cfg.package.version "21") (upgradeWarning 20 "21.05"));
 
       services.nextcloud.package = with pkgs;
         mkDefault (
@@ -378,14 +402,13 @@ in {
               nextcloud defined in an overlay, please set `services.nextcloud.package` to
               `pkgs.nextcloud`.
             ''
-          else if versionOlder stateVersion "20.03" then nextcloud17
           else if versionOlder stateVersion "20.09" then nextcloud18
           # 21.03 will not be an official release - it was instead 21.05.
           # This versionOlder statement remains set to 21.03 for backwards compatibility.
           # See https://github.com/NixOS/nixpkgs/pull/108899 and
           # https://github.com/NixOS/rfcs/blob/master/rfcs/0080-nixos-release-schedule.md.
           else if versionOlder stateVersion "21.03" then nextcloud19
-          else nextcloud20
+          else nextcloud21
         );
     }
 
@@ -443,6 +466,7 @@ in {
               'dbtype' => '${c.dbtype}',
               'trusted_domains' => ${writePhpArrary ([ cfg.hostName ] ++ c.extraTrustedDomains)},
               'trusted_proxies' => ${writePhpArrary (c.trustedProxies)},
+              ${optionalString (c.defaultPhoneRegion != null) "'default_phone_region' => '${c.defaultPhoneRegion}',"}
             ];
           '';
           occInstallCmd = let
@@ -591,6 +615,14 @@ in {
               access_log off;
             '';
           };
+          "= /" = {
+            priority = 100;
+            extraConfig = ''
+              if ( $http_user_agent ~ ^DavClnt ) {
+                return 302 /remote.php/webdav/$is_args$args;
+              }
+            '';
+          };
           "/" = {
             priority = 900;
             extraConfig = "rewrite ^ /index.php;";
@@ -609,6 +641,9 @@ in {
               location = /.well-known/caldav {
                 return 301 /remote.php/dav;
               }
+              location ~ ^/\.well-known/(?!acme-challenge|pki-validation) {
+                return 301 /index.php$request_uri;
+              }
               try_files $uri $uri/ =404;
             '';
           };
diff --git a/nixos/modules/services/web-apps/nextcloud.xml b/nixos/modules/services/web-apps/nextcloud.xml
index 6cbfda118c4..83a6f68edcb 100644
--- a/nixos/modules/services/web-apps/nextcloud.xml
+++ b/nixos/modules/services/web-apps/nextcloud.xml
@@ -11,7 +11,7 @@
   desktop client is packaged at <literal>pkgs.nextcloud-client</literal>.
  </para>
  <para>
-  The current default by NixOS is <package>nextcloud20</package> which is also the latest
+  The current default by NixOS is <package>nextcloud21</package> which is also the latest
   major version available.
  </para>
  <section xml:id="module-services-nextcloud-basic-usage">
diff --git a/pkgs/servers/nextcloud/default.nix b/pkgs/servers/nextcloud/default.nix
index a40dd71fafd..8205f4f860a 100644
--- a/pkgs/servers/nextcloud/default.nix
+++ b/pkgs/servers/nextcloud/default.nix
@@ -31,24 +31,19 @@ let
     };
   };
 in {
-  nextcloud17 = throw ''
-    Nextcloud v17 has been removed from `nixpkgs` as the support for it will be dropped
-    by upstream within the lifetime of NixOS 20.09[1]. Please upgrade to Nextcloud v18 by
+  nextcloud18 = throw ''
+    Nextcloud v18 has been removed from `nixpkgs` as the support for it was dropped
+    by upstream in 2021-01. Please upgrade to at least Nextcloud v19 by
     declaring
 
-        services.nextcloud.package = pkgs.nextcloud18;
+        services.nextcloud.package = pkgs.nextcloud19;
 
     in your NixOS config.
 
     [1] https://docs.nextcloud.com/server/18/admin_manual/release_schedule.html
   '';
 
-  nextcloud18 = generic {
-    version = "18.0.10";
-    sha256 = "0kv9mdn36shr98kh27969b8xs7pgczbyjklrfskxy9mph7bbzir6";
-    eol = true;
-  };
-
+  # FIXME(@Ma27) remove on 21.05
   nextcloud19 = generic {
     version = "19.0.6";
     sha256 = "sha256-pqqIayE0OyTailtd2zeYi+G1APjv/YHqyO8jCpq7KJg=";
@@ -61,4 +56,9 @@ in {
     version = "20.0.7";
     sha256 = "sha256-jO2Ct3K/CvZ9W+EyPkD5d0KbwKK8yGQJXvx4dnUAtys=";
   };
+
+  nextcloud21 = generic {
+    version = "21.0.0";
+    sha256 = "sha256-zq2u72doWhGvxbI7Coa6PHvQp7E41dHswFJiODZV8fA=";
+  };
 }
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 45802dd9f4e..9b9a68dbb13 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -6580,7 +6580,7 @@ in
   grocy = callPackage ../servers/grocy { };
 
   inherit (callPackage ../servers/nextcloud {})
-    nextcloud17 nextcloud18 nextcloud19 nextcloud20;
+    nextcloud18 nextcloud19 nextcloud20 nextcloud21;
 
   nextcloud-client = libsForQt5.callPackage ../applications/networking/nextcloud-client { };