@TheFinn@discuss.tchncs.Gmail may have worked with Kmail occasionally in the past. I think sometimes that involved going back to your Google account and telling it to accept an “unsecure” app. To be honest, I wouldn’t do that for an email app.
Elementary has the same problem with its mail app.
@Bro666 I tried it on Fedora 40 with Plasma 6. Don’t know if it’s broken there or not. In any case, the account wizard repeatedly showed me a screen with only a back and quit button when the account hadn’t yet been created.
Also kept telling me I had set up 2 accounts and asking if I’d like to unify them.