Driving in L on highway for 2 hours. Has any damage been done to the engine or transmission?
Definitely not. L is an increased regeneration braking mode that doesn’t really matter at steady speeds at all. The increased regen mode is to allow greater engine braking to put energy back into the batteries. You might use this in stop and go traffic or driving down a long mountain pass to keep from using the brakes so much (or at all). There is a paddle behind the left steering wheel post to momentarily increase that amount of re-gen braking.
All this must be in the owners manual. I’d suggest you read up on these neat features to maximize your use of the electric drive and improve your fuel efficiency. Be Happy, Drive On, no harm done!