OK, I think I have been down too many rabbit holes today researching contactless payment in London, some day trips and 2 longer journeys in April. Tell me if I am missing anything or have something wrong.
There is contactless payment available on both TFL and some of the National Rail providers but the contactless method differs.
TFL contactless can be either via Oyster (have an old one with money on it I will use up first) OR via CC with contactless properties OR via smartphone Apple Pay. I'd tap in and out on the turnstiles the way you always do with an Oyster card.
National Rail depends on the operator and maybe the route?
Day Trips: The specific routes I'm researching are to Bletchley (North Western Rail supports both m-Ticket and e-ticket to this destination) and Windsor and Eton Central (Great Western from Paddington which also supports m-Ticket, e-Ticket and Smartcard which seems like overkill for just one train ride so far). Both of these are outside the zone for the Oyster contactless system so I can't use ApplePay on them. I'd have to buy a ticket online on the app and would want to book ahead for the best prices.
Longer journeys: London to Harrogate and then York back to London OR Windsor. London to Harrogate from KGX on LNER supports m-ticket and e-ticket for either route (via York with a change or direct to Harrogate with several stops which is probably what I'll do. York to London or Windsor is back on LNER with a change to Great Western if I go on to Windsor both of which support m-ticket and e-ticket. Neither support Applepay but there is a huge advantage to booking ahead on these anyway.
As an aside it also looks like if I split the ticket on the York to Windsor trip it's slightly less expensive but I'll look at the times and prices when they are finally posted for April.
Thanks for any help in making sure my brain is untangled, lol!!