Qonto is French and so is the commenter on Twitter.

What you are saying is not correct; perhaps you are confusing it with the right to an account?

https://www.banque-france.fr/fr/a-votre-service/particuliers...

Yes, exactly. French citizens have an inalienable right to a checking account, enforced by French government. I don't remember the exact law, but I know someone who was 'interdit bancaire' (took too much revolving credits in the 90s) and the local bank _had_ to let him open a new account (a very limited one).