I have a really old keypair. Pre npub usage/adoption. It doesn't let me put it into the field. Not sure if that's a bug or feature on your end, but just a heads up.
It supports 64 chars of hex or the npub format. Which do you have?
I've been using this as my pubkey.
...can I just switch to the npub version of that, without confusing apps and relays and followers?
I think my npub is/would-be : npub144d2kklgswjhr63hkgcumxtdxafzua7s7ysuah7k0paerkzgy68qurzyy7
I used @rot13maxi's tool just now.
It's valid when I enter it on my end. Make sure there's no whitespace or anything extra in the field.
And yes, the npub is just a difference encoding.