I thought Apple does tell you how long they'll support hardware.
For example: https://support.apple.com/en-us/102772
That's not how long they will provide software support. It's how long you can get a hardware repair. Some "vintage" products will get current software support but not others. Some products have lost software support before even reaching "vintage" like the first Gen iPad.
That page shows "vintage" products, which is a category they apply after "5 to 7 years". It describes replacement parts and (bought) maintenance service in store locations.
They don't state how long they will provide software updates.