On Roblox it looks perfectly fine, but when you try it on it looks really weird. The edges aren’t straight and some of the text is unreadable. (I’m currently using Gimp on it’s latest version in case you were wondering.)
What solutions have you tried so far?
I scaled the image to a size less than 1024 x 1024.
I scaled the image to a size more than 1024 x 1024.
I tried exporting the image from a different program. (Photopea)
ROBLOX automatically scales your images, in the case of shirts, it’ll scale it to the size goal automatically. You could have a 2048x2048 square image and upload it and it’ll consistently look the same; though if you uploaded a 256x256 square image it’d be more pixelated. So whatever it has to do to get it to the needed size, it’ll do.
I count on ROBLOX updating this in the future and allowing us to upload higher resolutions; especially with PBR textures. I texture in 4096x4096 and to have the detail destroyed sucks.
I also wanted to add that it gets pixelated because the image is no longer in 2D form. All your t-shirts/shirts will look more accurate on the website than when they render in a game.