mrnaterpg Could you do me a favour please and try this? :

(Please do these commands in order)

composer remove fof/upload
php flarum migrate
php flarum cache:clear
composer require fof/upload
php flarum migrate
php flarum cache:clear
php flarum extension:enable fof-upload

      katos Here is the result when reloading the page after doing each command in that order:
      'Flarum encountered a boot error (Error)
      Class "FoF\Upload\Extend\SvgSanitizer" not found
      thrown in /var/www/html/dcs_flarum/vendor/fof/upload/extend.php on line 112
      Error: Class "FoF\Upload\Extend\SvgSanitizer" not found in /var/www/html/dcs_flarum/vendor/fof/upload/extend.php:112
      Stack trace:
      #0 /var/www/html/dcs_flarum/vendor/flarum/core/src/Extension/Extension.php(373): require()
      #1 /var/www/html/dcs_flarum/vendor/flarum/core/src/Extension/Extension.php(139): Flarum\Extension\Extension->getExtenders()
      #2 /var/www/html/dcs_flarum/vendor/flarum/core/src/Extension/ExtensionManager.php(390): Flarum\Extension\Extension->extend()
      #3 /var/www/html/dcs_flarum/vendor/flarum/core/src/Extension/ExtensionServiceProvider.php(31): Flarum\Extension\ExtensionManager->extend()
      #4 [internal function]: Flarum\Extension\ExtensionServiceProvider->Flarum\Extension{closure}()
      #5 /var/www/html/dcs_flarum/vendor/flarum/core/src/Foundation/Application.php(329): call_user_func()
      #6 /var/www/html/dcs_flarum/vendor/flarum/core/src/Foundation/Application.php(270): Flarum\Foundation\Application->fireAppCallbacks()
      #7 /var/www/html/dcs_flarum/vendor/flarum/core/src/Foundation/InstalledSite.php(151): Flarum\Foundation\Application->boot()
      #8 /var/www/html/dcs_flarum/vendor/flarum/core/src/Foundation/InstalledSite.php(82): Flarum\Foundation\InstalledSite->bootLaravel()
      #9 /var/www/html/dcs_flarum/vendor/flarum/core/src/Http/Server.php(59): Flarum\Foundation\InstalledSite->bootApp()
      #10 /var/www/html/dcs_flarum/vendor/flarum/core/src/Http/Server.php(36): Flarum\Http\Server->safelyBootAndGetHandler()
      #11 /var/www/html/dcs_flarum/public/index.php(26): Flarum\Http\Server->listen()
      #12 {main}'

          mrnaterpg hmm, ok - please disable it again for now and I will do some digging into this for you.

            mrnaterpg Can you try this for me, sorry?

            composer clear-cache
composer dump-autoload

            then try and run:

            composer require enshrined/svg-sanitize
php flarum cache:clear
php flarum migrate

            and see if fof/upload then works for you please?

              It must've been related to the MariaDB version. I updated my server so I could get mariadb updated an lo and behold the plugin seems to be working