So when I press the "Withdraw" button,
will the mBTC amount be transferred immediately to my registered address?
Or do I have the opportunity to review the planned transaction before it is finally published?

2021-10-04 ...
... you can request a withdrawal and they'll be processed in approximately 24 hours. Your statistics page will show a list of pending and completed payouts, including transaction id with the payment is released. The pending payout will show the address where the payment will go to. Please check this and if it is not correct, contact the pool admins immediately.