Where are you located? Privacy.com were first to bring this feature to the mainstream as a product but it exists as an add-on in various places. For example, in the UK it’s offered by Monzo and offered by Revolut in the many countries they operate in. If you want to use virtual cards, it should be possible where you live.

Wise (formerly Transferwise) also offers virtual debit cards. I don't think you can limit the amount or merchant, but it still works if all you need is to be able to cancel a card on-demand.

While virtual cards are technically a thing in Canada (e.g. you get a virtual cards if you add a card to Apple Pay), I’m not aware of any services that let you generate more than one at a time in a useful way.