Comment by qrobit

FWIW, these uBlock Origin rules solve the ploblem:

    ||accounts.google.com/gsi/iframe
    ##iframe[src^="http://accounts.google.com/gsi/iframe"]
    ##iframe[src^="https://accounts.google.com/gsi/iframe"]
    ##iframe[src^="//accounts.google.com/gsi/iframe"]
    ###credential_picker_container

source: https://stackoverflow.com/a/78429389. Last rule is from me since popup was invisible but still blocked the content underneath.