Re: If you can not enter the new password of the device's Google account, no Google service will work - including fetching mails by AquaMail.
That's what you wrote above and I believe you
Makes sense. Haven't tried it myself personally.
My main point was that for a Gmail account, Aqua Mail doesn't use or even know the password, and so it's not necessary to re-enter it, and it doesn't magically obtain the actual new password somehow either.