> Do they get paid per ARM chip sold, or yearly for the rights to sell ARM chips, etc?

Both. Basically at the top end You have licensing that big companies like Apple pay a large one-off sum ( comparatively large from ARM's perspective , but tiny in Apple's view ) for the use of ARMv8. ( i.e You will need to pay again for ARMv9 or ARMv7 ), and do custom design with the Instruction Set as along as it remain compatible with ARMv8. At the bottom end you are simply buying a blueprint from ARM, add some other IP you want and pay per ARM chip.

Anandtech has an article [1] about it and most of it are still relevant.

Since we are taking about business It is also worth mentioning the revenue of ARM before Softbank acquisition was less than the Net profits of Intel.

[1] https://www.anandtech.com/show/7112/the-arm-diaries-part-1-h...