Phone/Tablets do not resolve via local DNS

Since today, my Android devices do not resolve local DNS names via my local PiHole.
In the Settings/Network/Advanced Settings, "Private DNS" was enabled. Disabled and, Firefox/[Network utilities](https://play.google.com/store/apps/details?id=com.myprog.netutils&hl=en)/[Ping Tools](https://play.google.com/store/apps/details?id=ua.com.streamsoft.pingtools&hl=en) can still not resolve "plex.lan" (Plex server) or "licht.lan" (Zigbee Gateway) or any other internal domain. Even with static IP settings, nothing works. Any clue where I can tell Android "Use the DNS server announced from DHCP"? The problem occurs on all my android devices simultaneous.
No problem on my Laptop or Workstation. | Wifi Settings | Ping Tools with custom DNS set | Ping Tools with "default" DNS server | | -------- | -------------- |--------| | | | | Note: The Ping Tool/DNS Checker test with the "default" server was done, when a static IP was configured, so there should be used the LAN internal DNS Server, but it clearly must use something else. Using Wireguard as a tunnel into my network works. But that can't be the solution when I'm already connected to my LAN. --- EDIT: The problem was not my Phones/Tablets, but my router that enabled IPv6 automatically and used the DNS Server from my Provider via IPv6