I've been able to follow bird.makeup accounts from my Mastodon account on mas.to. It works great.
I tried to follow some from my personal GoToSocial instance. I can search with my client and click the "follow" button just fine, but the follow never completes. There doesn't seem to be any return connection from bird.makeup to my instance.
It's not clear if the issue is with GoToSocial or with bird.makeup. I've logged a bug report with GotoSocial here: https://github.com/superseriousbusiness/gotosocial/issues/1340