you can play at 4k full screen but game internally still can run 1080/1440
then you can enable image sharpening in your LCD or via GPU driver.

i never play games at exclusive fullscreen mode due to slow alt-tab switching.

Yes if you sit close to your LCD

if you plays on big TV, and sit further away, i doubt you can see the difference
even if the resolution reduce by 0.8 or further, post processing filter such as DLSS/FSR and other sharpening filters are there to compensate the detail loss.

i understand that, at one time, i had 2 LCD and 1 TV,
pretty much fully utilize my system , but at what cost? in order to achieve it i have to use Highest end GPU.

then the crypto boom came and i wasn't able to upgrade my system for years lol
i sold my pc due to its age and lazy to pursuit the PCMR dreams again, now i as long as my lappy can play 2 games at the same time without blowing up, im good with it