Are you sure you’re logged into your VRChat account?
Please hit Logout in your System menu, and log back using your VRChat account. Steam accounts cannot upload or use custom avatars (but they can use avatar pedestals).
Are you using the right Unity version?
You must use Unity 2019.4.29f1 as described in the VRChat Documentation. Any content uploaded from a newer version of Unity will not be visible in menus.