I think I finally found a solution.
One problem was that the device was connected via WLAN. Don't know if it was a response time issue or something else. At least now the update fuctions from RA work as intended.
Which probably was the problem with LB didn't start games. Because Retroarch was not able to download the appropriate core when importing roms.
Another problem that popped up after this was that most mega bezel shaders didn't work on that device although working on my other pc.
-> Soltion here was on that specific hardware the shaders only work with d3d11 or glcore NOT vulkan... which was my goto video driver. Now going with glcore because d3d11 had some frame glitches.
Emu Movies issue was also fixed by conntecting with LAN directly instead of WLAN.
What's still persisting is that LB still can't download RA in this setup, but installing it manually worked because not pointing to the install directory wasn't the problem but the failing of downloading cores as mentioned above.
So hope thiss helps if someone encounters same problems.
