Canonization is mostly considered to be under the remit of Papal Infallibility, which means it cannot be revoked. If the Pope gets drunk on sacramental wine and saints Pikachu the Pokeman character, Pikachu (somehow) enters heaven. Doubt that, and you commit heresy.

But that's not absolutely, totally decided RC law - just a majority opinion. AFAICT.

What absolutely has happened is that saints without plausible historical backing have had their feast days revoked, and (sometimes but not always) have been removed from the lists of saints the Church encourages Catholics to pray to. (St. Christopher is now believed to be allegorical, but prayer to "him" is still encouraged nonetheless.) Basically, they've been demoted, like the uncle that is technically still a blood relation, but doesn't get the invite to Thanksgiving dinner.

Now please pass the Turkiye.