DNS for remote LAN internal suffix not working

Hi, I’m new to tailscale, but pretty happy to get up a VPN so easily :slight_smile: but I have almost none knowledge on DNS, which is why I seem to struggle.
I use my OpenWRT Router with tailscale package to enter my LAN from remote locations using my Android smartphone or my Ubuntu Laptop.

Pinging the LAN IPs of other private devices works fine, but unfortunatly I struggle to setup the DNS correctly. The LAN DNS suffix (e.g. .xyz) is managed by the OpenWRT and offers static leases to some of the private devices.
At tailscale webfrontend, I added DNS - Nameservers with: Internal LAN IP, Split DNS, and Search Domain “xyz”.

But if I try to open e.g. a webfrontend of a private device by opening it’s name.xyz as registred at the router, I sadly don’t get a name resolution :slightly_frowning_face:
Can anybody please point me on how to debug what breaks the DNS lookup? I guess there are a lot of possible options that might prevent OpenWRT from offering DNS via tailscale interface or to propagate the new (internal) DNS to connected nodes :thinking: