luceos I posted a bit of the error a couple of weeks ago. This is what it says now, after giving it another go:
[2021-09-23 14:47:04] flarum.ERROR: TypeError: Flarum\Forum\Auth\ResponseFactory::make(): Argument #2 ($identifier) must be of type string, null given, called in /var/www/flanew3/vendor/fof/passport/src/>
Stack trace:
#0 /var/www/flanew3/vendor/fof/passport/src/Controllers/PassportController.php(94): Flarum\Forum\Auth\ResponseFactory->make()
#1 /var/www/flanew3/vendor/flarum/core/src/Http/RouteHandlerFactory.php(41): FoF\Passport\Controllers\PassportController->handle()
#2 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ExecuteRoute.php(27): Flarum\Http\RouteHandlerFactory->Flarum\Http\{closure}()
#3 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ExecuteRoute->process()
#4 /var/www/flanew3/vendor/fof/stopforumspam/src/Middleware/RegisterMiddleware.php(101): Laminas\Stratigility\Next->handle()
#5 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): FoF\StopForumSpam\Middleware\RegisterMiddleware->process()
#6 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ContentTypeOptionsHeader.php(21): Laminas\Stratigility\Next->handle()
#7 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ContentTypeOptionsHeader->process()
#8 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ReferrerPolicyHeader.php(30): Laminas\Stratigility\Next->handle()
#9 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ReferrerPolicyHeader->process()
#10 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/FlarumPromotionHeader.php(30): Laminas\Stratigility\Next->handle()
#11 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\FlarumPromotionHeader->process()
#12 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ShareErrorsFromSession.php(57): Laminas\Stratigility\Next->handle()
#13 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ShareErrorsFromSession->process()
#14 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/CheckCsrfToken.php(36): Laminas\Stratigility\Next->handle()
#15 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\CheckCsrfToken->process()
#16 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ResolveRoute.php(67): Laminas\Stratigility\Next->handle()
#17 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ResolveRoute->process()
#18 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/SetLocale.php(51): Laminas\Stratigility\Next->handle()
#19 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\SetLocale->process()
#20 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/AuthenticateWithSession.php(31): Laminas\Stratigility\Next->handle()
#21 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\AuthenticateWithSession->process()
#22 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/RememberFromCookie.php(52): Laminas\Stratigility\Next->handle()
#23 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\RememberFromCookie->process()
#24 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/StartSession.php(61): Laminas\Stratigility\Next->handle()
#25 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\StartSession->process()
#26 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/CollectGarbage.php(46): Laminas\Stratigility\Next->handle()
#27 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\CollectGarbage->process()
#28 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ParseJsonBody.php(28): Laminas\Stratigility\Next->handle()
#29 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ParseJsonBody->process()
#30 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/HandleErrors.php(57): Laminas\Stratigility\Next->handle()
#31 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\HandleErrors->process()
#32 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/InjectActorReference.php(25): Laminas\Stratigility\Next->handle()
#33 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\InjectActorReference->process()
#34 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(76): Laminas\Stratigility\Next->handle()
#35 /var/www/flanew3/vendor/middlewares/request-handler/src/RequestHandler.php(84): Laminas\Stratigility\MiddlewarePipe->process()
#36 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Middlewares\RequestHandler->process()
#37 /var/www/flanew3/vendor/middlewares/base-path-router/src/BasePathRouter.php(101): Laminas\Stratigility\Next->handle()
#38 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Middlewares\BasePathRouter->process()
#39 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Middleware/OriginalMessages.php(36): Laminas\Stratigility\Next->handle()
#40 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Laminas\Stratigility\Middleware\OriginalMessages->process()
#41 /var/www/flanew3/vendor/middlewares/base-path/src/BasePath.php(73): Laminas\Stratigility\Next->handle()
#42 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Middlewares\BasePath->process()
#43 /var/www/flanew3/vendor/flarum/core/src/Http/Middleware/ProcessIp.php(24): Laminas\Stratigility\Next->handle()
#44 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/Next.php(51): Flarum\Http\Middleware\ProcessIp->process()
#45 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(76): Laminas\Stratigility\Next->handle()
#46 /var/www/flanew3/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(65): Laminas\Stratigility\MiddlewarePipe->process()
#47 /var/www/flanew3/vendor/laminas/laminas-httphandlerrunner/src/RequestHandlerRunner.php(96): Laminas\Stratigility\MiddlewarePipe->handle()
#48 /var/www/flanew3/vendor/flarum/core/src/Http/Server.php(44): Laminas\HttpHandlerRunner\RequestHandlerRunner->run()
#49 /var/www/flanew3/public/index.php(26): Flarum\Http\Server->listen()
#50 {main}