Board Game Arena

When dealing need cards to players, how is the card deck handled? Is the entire deck shuffled each round? Or does the implementation keep track of the cards that have been played, and set those aside. Only adding the discarded cards and shuffling whenever there are no more cards in the deck?

If you're asking about the official rules, it's in the rulebook (English Rulebook, page 11):

Note: Players can all draw their cards simultaneously, but if
someone thinks it matters, you should draw cards in order,
beginning at the Starting Player Token and proceeding clockwise. If a deck runs out of cards, you shuffle its discard pile to
make a new deck. In some situations, drawing before or after
this shuffle might be important.

If you're asking about the BGA implementation, do you have reason to suspect that it's not following the official rules?

"someone thinks it matters, you should draw cards in order"

that part is not implemented, the need assignment phase is simultaneous so however does it first - draws first and you cannot force it to wait.