Simply put: Freeze is usually a temporary hold that you can undo if you find the card.
Key points
Block can be used to temporarily or permanently disable the card, depending on the bank's policy.
Cancel/Close means the card is permanently deactivated and will not be reactivated with the same information.
The terminology varies between banks, so in case of actual theft, don't rely solely on the button's name in the app; contact your bank and report the card as "lost/stolen" so they can follow the correct procedure and determine if you need a replacement.