If you run which flyctl … what does that say? Only regardless of any auth issue, flyctl versionshould work. That’s the first thing to fix. And if it did, the auth would probably too.
Did you install it using their build script? Install flyctl · Fly Docs Maybe grab the latest version by doing that and see if that alone helps.
I don’t know how the install script is doing that - one for @michael ! - but in the meantime I’d think you could download the latest binary directly, from Releases · superfly/flyctl · GitHub
That should work. And that should fix your login issue too.