Did more testing over time (prob 14 hrs later from last post), and still got banned with 300 gem, 20k gold, but also 100/40MP since this mod also makes spending MP increase. I think it does do server check either after closing the game, during launch, or during a set "maintenance" time like 12AM. There is a statistics button showing how much you earned and bought/sold and a bunch more stuff. However doesn't seem to be a line where it shows how much you spent, but probably is there and hidden from the menu. Likely have to keep gems below 100 and gold maybe under 5k, which makes the mod very limited use. Extremely low rate of attaining gold (like +5g every monster kill) is also likely another factor so it's supposed to be crazy hard to make any progress in this game if you were to go legit.
Needs a mod deactivator mid-game so you can spend down what you hacked, otherwise ban. The "can buy even if you have 0 money" like harry potter hogwarts mystery mod would be a good workaround probably if it's possible.