Do you have the Proton Bridge installed?
It’s really quite simple, login to bridge with same user/pass that you use on the webmail. Select the account you wish to configure from the drop down and it gives you the complete configuration. Then you just open your preferred and add a new acct with just a few copy/pastes and you should be up and going in no time.
Note the password when using Bridge to local mail client is different then when logging into the webmail page.
As for Brave there is a great little script here: