@doesnm So the user should then set nick = _@domain.tld in the twtxt.txt?

It seems more intuitive and userfriendly to just use: nick = domain.tld and have then convention for clients to render the handle as @domain.tld instead of @domain.tld@domain.tld

For a feed with no nick defined (eg. https://akkartik.name/twtxt.txt) it will also be simpler and make more sense to just use the domain as the nick and render it as @domain.tld