The wording is a bit weird, but I'll try to explain what's actually happening here;
This is referring to the pixel's under screen fingerprint reader. Since it's an optical reader, it needs light to see what it's reading so it blasts a white circle around the reader. Currently if the screen is off (we'll get back to this in a sec) then it can't turn this circle on to read the finger. Basically there's an "off" and a "black" with oleds, they'll look identical, but If the screen is "off" you won't be able to light up a section. This can occur when the always-on-display is active, but not if it's disabled. From what I gather this leaves the display in an "black" state so it can still light up the reader, even if AOD is disabled
Also totally accidentally sent this when trying to check the MD ob "off", hopefully you haven't checked this message yet lol
I've never had a phone that had one mounted anywhere other than the front, so under screen was natural muscle memory progression for me compared to side or back mounted.
I am curious of what you dont trust and why