Bank told me before whether save or not once use the card automatically saved orh

for sake of convenience once you register tour CC / DB to shopee/lazada they only ask OTP one time. then the subsequent transaction does not require OTP.

it will only ask for OTP after every few months.

convenient yes, secure no.

so after finish transaction delete your card from the platform.
lazy = high risk.

It's possible. There's a disclaimer when you add the card that an OTP may not be needed for purchase and you have to agree with it if you want to add the card in. Used to be that only Lazada did that, but seems like Shopee is doing it now.

I just purchased a few days ago using PBB card and no OTP was needed for Shopee.