Gregory's Server@itchio heads up that Mastodon/Fediverse addresses can't always be directly mapped to URLs eg. the URL for @tentaclehead has an added subdomain https://mastodon.indiegames.online/@tentaclehead which I think would require a webfinger request to translate
@brook Our goal was to address the most common use-case since many people are moving their socials around right now. In the future we may revisit with broader support for more fediverse platforms. If our implementation doesn't work for you, you can also put an http link in your profile's content