Why does my German bank account take days to process debit card transactions?

Whenever I make a purchase with my German debit card, the amount isn’t debited from my account immediately. It often takes a few days, which sometimes causes me to forget about the expense and gives me a false impression of how much money I actually have. This doesn’t happen when I use my Wise or Revolut cards. Why is that?

Ps: I use commerzbank