Recent versions of photon should improve this (2.0). Based on what you posted before, you're using an instance hosting an old version of Photon. (this sort of thing is why I complain about instances hosting photon a lot)
Photon uses some obscure Lemmy API things to download images that actually fit the screen so you aren't wasting tons of bandwidth on 4k images on a 32x32 profile picture.
As far as I know, no other client does this when it really should. Because of this, Lemmy doesn't really support what I do all that well, and so the downscaling algorithm Lemmy uses causes images to look really low quality.
Are you using phtn.app or some instance's hosting of it?