This is basically a case of Catholics wanting to deny the full observance of their faith to a (crypto) Jew, based on them believing that this person does not follow their faith (abortion is highly contentious issue among Catholics of both sexes).

So I wondered if the reverse was true... and of course it is, but here's some detail:

It is forbidden for a gentile to fully observe Shabbat... [a gentile in the synagogue should] decline any honors that are offered to you... they can't count you in the minyan

A non Jew is not allowed to keep Shabbos

The Torah says "a Gentile is forbidden to observe the Sabbath or to make a Sabbath of their own"

You may disagree that Biden is a crypto Jew, but his Catholicism is certainly a farce - observed for politics only.