I had this problem with 2.4.3 and just updated to 2.4.8 and still have the problem.

As admin I changed the avatar size for users to a smaller size. From that point on I no longer see the option to tick the box to delete a user's avatar for users with the new smaller size.

Even new users, If I go to edit their profile in the user administration their avatar does not show and the delete box does not show

If I go to (edit user) for a user that still has the larger size avatar, the avatar and delete box shows as normal and I can delete their avatar

Is this how it's meant to work? I thought you could always delete any user's avatar from the edit user page?