Resetting settings either UI for user or system wifi for the system

I have a user where I am no more happy with UI settings i.e. many UI elements are displayed too big, but I can't recapitulate where I set them.

I have created another user where the UI settings are default so I am very happy but as it seems the wifi settings are global with regards to saved network names but not the passwords. The problem is now that I can't set passwords - as I go to "edit" in the Network Manager, it freezes.

Any ideas what to do? I use Xubuntu 20.04. Maybe there is a more advanced and stable Ubuntu software to managed network connections than the default one?