[Milhouse]

My question: Is it possible to run newest Kodi 18 testbuilds with older Kernelversions? If yes: how

Sure - downgrade the kernel in git to whatever version you need then compile LibreELEC.

Edit: you'll need to go back a long way to avoid the bug - it's in 4.9.y: https://www.spinics.net/lists/linux-medi...21356.html 

 Thank you for your answer. How do I downgrade the kernel in git? So far i have been able to follow the instructions from https://wiki.libreelec.tv/compile#tab__f...hub_master . A Server is set up and running. Do i have to edit the package.mk file in /packages/linux or is there a better way to downgrade? Thanks in advance.

Yes, you need to edit the package.mk back to 4.9.y, and fix any build issues (including reverting kernel patches, kernel firmware) that may result from using an older kernel. If you need more assistance I suggest opening a thread on the LibreELEC forum as continued discussion is off topic for this test thread.