Mastodon has a nice feature where you can prove ownership of a link in your profile by setting a backlink on it (implying you at least control the content of that page).
So, if you don't want to set up your own Mastodon instance under your domain, you can instead link your Mastodon account to your homepage running on a domain of your choice. It's not something I bother to do, because I'm nobody important, but if I was e.g. Taylor Swift or something, I could show that my Mastodon account was affiliated with www.taylorswift.com, and thus give you a pretty good idea that I'm actually the real deal.
From the Edit Profile page on Mastodon (v3.5.3):
> You can verify yourself as the owner of the links in your profile metadata. For that, the linked website must contain a link back to your Mastodon profile. The link back must have a rel="me" attribute. The text content of the link does not matter.
