You will need new Cases for every new iPhone 13 model (no 12 Series compatibility) : r/iphone
Ace Pro® Case with MagSafe, iPhone 13 Pro Max
Will an iPhone 12 Pro Case Fit on the new iPhone 13 Pro? - ESR Blog
Best iPhone 13 and iPhone 13 Pro cases
Will an iPhone 12 Case fit an iPhone 12 Pro - Caseface
An ultra thin case for the iPhone 12 Pro. This incredibly light and slim case is the thinnest iPhone 12 Pro case. It adds grip but feels almost invisible. It's thin, stylish, and branding-free.
totallee Thin iPhone 12 Pro Case | Pacific Blue
Do iPhone 12 Pro cases fit the iPhone 13 Pro?
OtterBox Vue Series+ Case for Apple iPhone 13 Pro Max and iPhone 12 Pro Max - Clear
LifeProof NEXT SERIES with MAGSAFE Case for IPhone 13 Pro Max & IPhone 12 Pro Max - PRECEDENTED GREEN : Everything Else