ok I fixed it thanks to help of OBS Discord. They pointed me to this thread:
https://forum.audacityteam.org/t/peaks-limited-between-0-5-and-0-5/42312/1
https://manual.audacityteam.org/man/faq_recording_how_to_s.html#rinstereo
I changed recording channel to Stereo and I can see the clipping using the View>Show Clipping ON/OFF and I can also use the ACX check which now reads 0db Fail as expected.
I have no idea why I had to change from Mono to Stereo, but as long as it works.
Thank you