[Ralf Jahns]

 You need to start kodi like that: KODL_GL_INTERFACE=GLX kodi (thx to fernet)T 

Thank you very much again for your help.
Hm, it's getting more difficult :-) I use LibreElec. Do I have to modify sytemd config files for that? How do I do that?
With hardware acceleration disabled, HD TV uses nearly 100% CPU load and playback is sometimes not flawlessly.

Best Regards
Ralf Jahns  

Yes - there is a posibility to do that. I pinged Milhouse on slack cause I have plain forgotten how to do that on LE :-)

Btw. HD is also mpeg-2 for you? Cause H264 should still work with VAAPI right? 

German public service broadcasting (governmental financed) TV stations encode HD with MPEG-4 (I think this is H264) and you are right, this still works with VAAPI. So it is possible to keep hardware acceleration for MPEG-4 switched on but meanwhile I did the setting you suggested to switch back to VDPAU.
Don't understand why all this is necessary. Is it a bug? Why is VAAPI enabled for my hardware if it doesn't work?

Best Regards
Ralf Jahns