I recently bought minecraft java edition but I am unable to use skins. I change the skin on the site correctly, but when I go to play, only alex's skin appears. I've seen other reports about this, but I didn't find the solution. Can someone help me please? (version 1.17.1)

(Only on public servers my skins are showing up.)

When I go to play in my friend's world, he's wearing a skin but I can't see it either.
He told me that someone else has already come to play in his world and she was skinned and could also see his skin.