The answer is not much physical effort at all, unless you count a short walk along a freshly strewn blue pine needle path from car drop off to the lodge via a few steps too much of a physical effort ie Ganthey. Paro which is slightly longer but it has an alternative less scenic route too.Punakha you need to cross a very manageable suspension bridge. Thimphu is virtually right at your doorstep.

ask for the rooms closest to the ground without the need to climb stairs .
Paro , Punakha and Thimphu rooms need more walking from the “lobby” but very manageable.

not been to Bumthang yet and it’s suggested one fly there instead as the car journey from the other lodges is the longest .

your friend on a donkey or horse is likely the one where you can hire a donkey to ride up to the Tigers nest monastery.at Paro. I didn’t bother with this climb.

Bhutan with Aman is almost effortless unless you decide to go on nature walks and water rafting .

Do go, it’s not to be missed .