Apple isn't "moving to Nvidia". Did anyone claim they were "moving to Softbank" a few years ago? The owner of the company that licenses the ARM ISA is irrelevant to Apple, they do their own designs and haven't used anything designed by ARM for a long time. They won't use anything designed by Nvidia, so nothing Nvidia does could really affect them - they can't change the terms of Apple's architectural license, raise prices, or deny access to Apple.
The only thing they could MAYBE do is if the license only covers the current ARM ISA and not future extensions, ARMv9, etc. then they could raise the price for adding those in the license. If the terms aren't to Apple's liking they could simply say "no thanks" and stick with the current ISA which is more than adequate for a long time to come.