Short answer:
pfp: 1:1: 250px x 250px
banner: 16:9: ~1920px x 1080px*
*Banner crop changes depending on screen size
PLEASE COMPRESS AS MUCH AS POSSIBLE - these aren’t auto compressed right now.
Profile banners are also used for vgen.co directory right now.
Note that gifs and animated webp / apng are supported for both.