As of right now, inputting 920x720 in a scratch thumbnail on uploads.scratch.mit.edu would instead show 480x360. Is it a bug, or did they phase it out?
My browser / operating system: MacOS Macintosh X 10.15.7, Safari 18.6, No Flash version detected

scratch never supported 720p in the first place tho

They recently changed how thumbnails are generated – they're now always 480x360. Previously, the resolution of the thumbnail would depend on your screen resolution.