If you see someone wearing an avatar you like, you can select their user profile, go to their Avatar tab, and if the avatar is public, you can select it and copy the ID from there.
If you want to save an ID without logging into the game, this is the best method. You must be logged into your VRChat account on the website. how to get avatar id vrchat
Click on the avatar you’re currently wearing. If you see someone wearing an avatar you