I have these 2 custom filters in Brave, and haven't seen this popup since:
##iframe[src^="https://accounts.google.com/gsi/iframe/select"]
||accounts.google.com/gsi/iframe/select^$third-party
##iframe[src^="https://accounts.google.com/gsi/iframe/select"]
||accounts.google.com/gsi/iframe/select^$third-party
accounts.google.com/gsi/$3p
Any substantial difference between the suggested two, and this one?