Ook so as said, I tried to replace the libs as mentioned, did not work.
Then I just went all in: replaced the whole libs folder in 20180109 with the one in 20171011 (where the recommended libs come from).
Flashed it and... tadaa! Video recording and playing with stock camera/gallery working.
So do I totally have no idea what I am doing? True. Did I maybe revert bugfixes done in new version or just screw up things in general? Very well possible!
However camera works and I can not find any new bugs after trying for a short while. So if anyone wants to try out, here is the modified zip:
h t t p s : / / www109.zippyshare.com/v/GiSSNgNZ/file.html
Just flash as usually. Let me know if this works!
Someone with more skill than me could probably find out what library is actually causing the issue (instead of just replacing all of them).
PS:
@New Macław, if you read this: Is a new build still an option? Or did you quit this phone for good? If you don't plan to develop for this phone any more, could you reconsider making the source public? I get that you did not want to publish when still developing, but if you don't develop any more for this device, what is the point in keeping it secret? Thanks for years of hard work you did for us!