You should not need it to enter a password in the field, only to view the current password. This is pretty standard behaviour in recent versions of Android: to view passwords you have to authenticate by going through the screen lock functionality - PIN, Pattern, Fingerprint. This is to protect against others viewing or stealing your passwords if they have access to your phone before screen lock kicks in. There is similar behaviour in (at least) Firefox and Firefox-based browsers on Android, and I don’t think it can be switched on and off in the app.
I think I recall this feature being added to K-9 a while ago (2 maybe 3 years) when people wanted to be able to see the password set for an account: other users, and the app maintainers believed that was a security risk and should only be possible with some form of protection, in this case screen lock. I don’t think it is possible to change this behaviour
For some history, and discussions about the implementation of this behaviour, see this thread. The original position of the maintainers was that password protection was not needed, bt they changed their opinion, and it got implemented in or around version 5.9