As often as you want BUT every card has a limit and the limit is assumed to be fully drawn on every card as well as your mortgage when you apply and provide the list of assets and liabilities to the lending (card issuer) organisation. If you have high limits on your cards your credit capacity will drop very quickly eg a $50K limit on an Amex platinum card. You will find that as you approach your credit capacity you will be rejected for new cards. So what to do?
Return cards you do not need and notify the lender to cancel the card.
Always request a low limit on the new cards you keep for everyday use.
ALWAYS pay your card bills on time as late payers get posted to the credit watch agency every time they are late since 2018. New applicants get checked out for late performance.
Finally; when you return a card after you have received your bonus points and the year is almost up; the card issuer will usually ask why you want to cancel the card. I always say I am buying a house and the mortgage provider has required me to reduce my credit exposure. The card staff always nod wisely and tell me to be sure to reapply to them when I am able to or decide to take on more debt .