What if all players choose to draw three cards in a seven hand, one deck game? There won't be enough cars will there?
Once the deck has run out, the cards already discarded are shuffled to make a new deck from which replacement cards can continue to be dealt to players. (https://www.pagat.com/poker/variants/5draw.html#:~:text=If%20the%20deck%20runs%20out,the%20player%20to%20dealer's%20left.)
Seven five card hands have been dealt. That leaves 17 out of 52.
There will be enough cards (15 out of 17) to accommodate the first five players. These players will return 15 cards in discards.
After the 16th and 17th cards are dealt to the sixth player, the 15 discards are shuffled, and one of those cards is dealt to the sixth player as the "18th."
Then three cards are dealt to the seventh players from the shuffled discards.