They were once required to do so (and may still be; I’m not sure at this point), at least if they want to offer flights to or from the US:

https://en.wikipedia.org/wiki/ATPCO

However, interpreting this data properly is decidedly nontrivial (>1M LoC).

Pricing does not imply booking is OK, though. And even circa 1999, Southwest hassled us (ITA Software) about even showing their fares, without us offering any way to book any flights on any carrier.

Displaying the fares in a separate website isn’t the problem. The resale of tickets is, since other aggregators need to pay Ryanair a license fee to resell, and Booking is avoiding that by using RPA

Ryanair does. The machine is yours running a browser.