Yeah I think its an issue on their end, I paused the video when he had the slider at the default (the middle), made sure my TV was at a reasonable backlight level, closed my curtains and turned off the lights. There was still a some light coming in around the curtains so its not pitch black but with those conditions I could juuust barely perceive the left triangle when head-on to the TV.
So in the proper dark at night I'm sure it'd be perfect. I think John uses an LG OLED to do his checks sometimes and if the game crushes blacks a tiny bit (that wouldn't be noticeable on a properly setup VA or IPS LCD due to them not being able to show the true brightness usually and they elevate it slightly) it can look really bad on an OLED thats set up to be really contrasty.
I was speaking to a guy in the youtube comments and he said he couldn't see it on his IPS monitor or OLED TV no matter his settings but then he checked on an IPS TV and he could see it so I think its a signal mismatch or something. LG OLEDs had the weird thing with the limited vs. full RGB range not being picked up by the Auto setting in the TV when used alongside the PS5's Auto setting.
TBH I'm completely unclear if this is in SDR or HDR, since John's wording is a bit confusing.
What display do you have
E
elliot5
?