@mitu
I just reinstalled alsamixer and now everything is working. still no idea what caused this issue. made a backup image of my sd card now. thx for ur replies bud, learned a little more about alsa✌🏽
You should add arm_64bit=0 to config.txt and reboot
Try adding PTR64=0 to the build options
That were the solutions.
I expect it will also work without using PTR64=0 now.
Compiling seems to be about 10 hours on a RPI4/8GB which is much better than 1 month on a PI0/1.
So now I have a working binary and channelf is working as expected ;-)
Will try some other systems later.