Steam implements TOTP with a different alphabet. The basic algorithm seems to be the same as usual TOTP, but the representation of the token is different. An example implementation can be found here: https://gist.github.com/mooop12/1af7f0ffc8f28ea76f27abcba1e6da01
It would be cool if Enpass added support for these token types (maybe even as part of Enpass 6? :-) )
To not clutter the UI, maybe you could take the road of Bitwarden which uses a URL scheme to support different token types (no schema = default TOTP token, special token however could be steam://xyz123abc456).