Issue node.js configuration in PLESK Obsidian 18.0.67 Update Nr. 3

[Heinrich]

Server operating system version

Ubuntu 22.04

Plesk version and microupdate number

Obsidian 18.0.67 Update Nr. 3

Hello everyone...

I ran Foundry VTT on my server in a subdomain: https://vtt.werwolf-live.de
It ran good on Monday, but I had trouble with other domains, so I ran plesk domain repair and seemingly changed stuff on this subdomain, too, for it doesn't work anymore today.

I tried to find a tutorials on how to set up node.js to re-check all the settings.
This one on the plesk pages mentioned to disable nginx reverse proxy: How to Host Node.js Applications on Plesk Obsidian

But if I check the logs from Monday, there is mentioned as source "SSL/TLS-Zugriff für Apache".
So, my guess is, that the reverse proxy was active (as it is on all other domains, too).
But, currently I get the error

400	GET /socket.io/?session=cbbf7f61edd19b65d4956a43&EIO=4&transport=websocket HTTP/1.0

And that is a apache error, too. Node.js doesn't seem to throw any errors, my guess is, it isn't even called, but the errors are happening before that. That is also the fact, that the static parts of the page seem to be serverd, but dynamic parts, like the login box do not appear (although it is visible in the preview of the domain, for some reason).
Currently my nginx is set to act as proxy, serve static data, and I have some additional Config for security (none of this was changed):
ssl_session_timeout 1d;
ssl_session_cache off;
ssl_session_tickets on;
ssl_session_ticket_key /some_path/nginx_ticketkey.rnd;
ssl_early_data on;
server_tokens off;
ssl_protocols TLSv1.2 TLSv1.3;
ssl_prefer_server_ciphers on;
ssl_ciphers ECDHE-RSA-AES256-GCM-SHA512HE-RSA-AES256-GCM-SHA512:ECDHE-RSA-AES256-GCM-SHA384HE-RSA-AES256-GCM-SHA384;
ssl_dhparam /some_path/dhparam.pem;
ssl_ecdh_curve secp384r1; # Requires nginx >= 1.1.0

There are no apache configs specific for the sub domain.

So, my question is.
Is the tutorial above acurate and nginx should redirect to node.js directly?
I tried to deactivate node.js and reactivate it, in plesk ui. It didn't fix the issue.
Neither did I get additional info be switching to development status, from production.

Does anyone have any ideas?
Thanks.

ps.: I did disable ModSecurity, thinking it may be the issue, but that didn't change anything either.