I've tried everything: changed root password, changed my user password, yet Chrome, Edge and Brave browsers still insist on using my old very lenghtly password.
How do I change it please?
Open Passwords > Login > find the old password and change it manually or remove it. Please copy and paste these passwords somewhere so that if new ones don't work you can restore the older ones. I have some passwords there that have weird characters so you may not be able to read some. If possible, maybe it's better to try changing the passwords directly from the browsers settings page, because as I don't use Passwords it can be only a password manager and I don't know if changing a password there means that the related service password will be changed.