Flying is a little better in this regard because you have many more competitors in ticket sales. Versus trains in Europe where you have the national rail of each country selling tickets plus just ~2-3 third party sites, and in many situations they are all broken (depending on countries involved).

There are dozens if not hundreds of airfare consolidator sites. Most of them are problematic. I can easily find some that do not block Tor so I can at least see the schedules and pricing. But then when I purchase a ticket, it’s often a shit show: I get a msg saying i have a ticket, then the next day i get a notice that my flight was cancelled for no reason (if i’m lucky; sometimes they don’t even tell me they cancelled the ticket). They never tell me why, but after probing it’s often that they don’t like my use of a disposable email address, or that I used Tor, even though the website rejects neither. So it’s a big effort to find the needle in the haystack that works but at least the possibility is there with air travel.

With train sites, consumers with properly defensive browsers are usually blocked from even seeing the fares on all ~2-3 sites that sell tickets. Then there are other shenanigans like online purchase only promos extra fees for cash acceptance.

But I have to say it’s never a plane vs. train choice for me. If I would normally take a train, then usually the bus is the best option w.r.t digital rights and privacy. If crossing the pond, then the flights Spain is cancelling are likely connecting flights for me. So it means I probably won’t be getting flights that connect in Spain unless Spain brings in train codeshares for airlines.