While you can be lazy driving an auto you can also drive it in much the same way as a manual just without having to use a clutch, after all most auto gearboxes are really “semi-auto” with a full auto mode(CVT not counted as it’s crap, personal opinion) but when using them in manual mode either with the shifter or paddles is just about as involving as driving a manual.
Having the option to drive this way when you have leg problems is great as it keeps you more active on long drives, I tend to switch to “M” on my journeys once I get into traffic or country lanes/built up areas etc and leave in “D” for the long motorway stretches, really makes a difference to your journey.