So you can deduct gambling losses up to your winnings. But Is there a dollar limit? If I win 50k, lose 40k could I deduct the full loss? As so on, in theory, to infinity?

yes. but understand winnings are reported on schedule 1  losses are deductible only if you itemize. - schedule A.

the only limit is that losses can not exceed winnings. TT would probably prevent you from e-filing if you claimed more.