I want to use my personal art as an avatar to make it match with my Discord and YouTube, but I don't want to post it as a public post. Is there any way to upload my art as a "private" post (nobody can see it except me) or use it without uploading?

No, as far as I'm aware there's no such thing as a "private" post.

All avatars need to be posts so that way people can't just bypass site rules with them.

definitelynotafurry4 said:
All avatars need to be posts so that way people can't just bypass site rules with them.

Yep, plus so that blacklists still work on them

e621 isn't a personal art website, it's a booru. Everything here except for sets is communal.

alright, i i'm gonna stay with lucario