Some decks do have extra major arcana cards beyond the standard 22. Tarot cards get printed on big sheets that can fit like 80 cards total (8x10 grid), so there's usually extra space anyway.
Here are some examples I can think of:
The Happy Squirrel became a thing in indie decks for a while after it showed up as a joke on The Simpsons lol.
Zeke's Arcana added a "Patron" card.
There's a Native American/indigenous deck out there with two extra major arcana cards.
Plenty of other decks have thrown in additional majors that fit their specific theme or vibe.
So yeah it's totally possible someone made a deck with a 23rd card called "The Unknown" or whatever. Creators do their own thing sometimes.
But just fyi, the traditional tarot structure only has 22 Major Arcana cards. That's the standard across most systems and traditions.
