The ENCTS bus pass is valid on all registered local bus services in England, with exceptions as defined by the relevant local authority of the route (or boarding point). Hence there is no overall list, but each LA will have one. They are valid between 9:30 and 23:00 Mon-Fri and all weekend. They are ITSO cards and should work on most ticket machines that take cards, but in practice many combinations of issuer and bus operator don't work reliably and they never scan in London. Local cards work on the local buses!
Local authorities may exclude routes from the scheme for various reasons, including tourist or special purpose routes, historic vehicle routes, primarily bookable coach routes, where the fare includes an amenity element like car parking, rail replacement, ... Conversely they also may include journeys at extended times, generally or specific journeys. e.g. I can use a specific 9am journey as it only runs once a week. The Trent Barton Red Arrow is allowed from Derby, but not from Nottingham - different county councils. Journeys crossing into Wales or Scotland get complicated, but may be allowed either way.
You can find the Acts of Parliament and read them if you want, but most issuing authorities have a simplified explanation in the bus pass usage section.
You have to ask locally for the variations.
