I am pushing the profile images of users thru api and it has restriction of 2MB. I am pushing 800x800 pixel image but some users uses large screens or meeting rooms and there their photo gets pixelated and does not look good.
Can I ask where you are displaying / seeing the blurry image? A screenshot would be great!
As for changing the upload resolution and restrictions, that is not handled by the API and App Marketplace team so I would suggest creating a ticket here: https://support.zoom.us/hc/en-us/articles/201362003