SteamLink usage over two VLANs

Hi everyone,

I asked if one of you guys ever dealt with an similar idea.

My current (and beloved) OpenWRT setup works with two VLANs. First is using a Mullvad VPN connection, second is not. As worked out together with this community's fantastic help I can also communicate between them (e.g. a Nextcloud server and a Pihole can be reached out of both of the VLANs). See here my setup (slightly adapted, but same infrastructure currently): Wireguard setup: Mullvad Client + Server for Android

Now I added a new Raspi, running RetroPi and SteamLink. It works great in the same VLAN. SteamLink then gives good latency and a "direct" connection. But if I set them in different VLANs (since TV is in non VPN zone for Video streaming and gaming PC of course uses VPN), even with setting a rule, which allows acces from both networks (like for the Nextcloud) it is not working well.

Rule looks like that (but seems to work fine):

config rule
	option dest ''
	option src ''
	option priority '8'
	option lookup 'main'

I can see the PC (Host) running the games on the SteamLink SW on the Pi, but connection is laggy and shown as something like "LAN@", so no "Direct". I think the network rules are fine. I found some reddit articles ( where it is soomehow solved using an "UDP Relay on port 27036" (never got in touch with that). Is something like this avaiable in OpenWRT as well? They seem to use pfsense there.

Thanks for any ideas!