When connecting to a remote share, for which I previously had a password saved (on plasma/frameworks 5), I was asked for the authentication credentials for it, and not given an option to save them. Maybe this belongs in kio?
Same, Dolphin 24.01.95, Plasma 6 RC2 I tested both smb and ftp: it just keeps asking password at every session and no option to save it
Fixed for me with smb:// locations on 6.0. No longer presents for user/pass, and logs in with saved credentials.