Lrt: i mean ppl still do that w low res images. Its just that its harder to tell if that tee you boight online is using stolen art or not because a b0t got their hands on a ultra HD 4k version online. Also the higher res the easier it is to edit out watermark.

Dont upload art at full resolution online.

You dont wanna get in a scenario where you have to be able to show proof that you made that inage but if you shared the original resolution/workfile/etc online then ppl can claim its theirs. Its prob a cery unlikely scenario but it is not impossible.

I understand cases where you have a VERY tall or wide image where being able to upload a larger dimension makes sense (lile webtoon pages). But if ppl can see enough from a small size of your artwork, no need to upload the full res.

Also remember that watermarks dont serve as protection from art theft. Its purpose is to make it possible for ppl to know WHO DREW THAT PICTURE that they found on some obscure image board five years ago.