There's a spectrum of mountain bikes.

You are likely shopping on the cheap end and that's a good place for your stated purpose. Just make sure you have a freehub not a freewheel, which usually means 8 speed not 7 speed in the rear.

if you want to upgrade from there, bikepacking or traditional touring rigs are extremely versatile.

A "real" trail bike with air fork and air shock on a complex rear suspension and a dropper seatpost is excellent at steep climbs and fast descents and you should definitely try one, they are fun as heck. But they're not great commuters.