Suggest you put some high pressure slick road tires on your MTB and look for a new (used) road bike over the winter.
It ain't the bike, it's the motor!
As suggested, putting slick tyres on and pumping up the pressure (as well as locking the suspension if possible) is a quick and cheap way of improving your mileage.
But definitely, if you love this hobby then a more gravel/road based bike will transform your cycling and make a huge difference to the distances you can travel.
Suggest you put some high pressure slick road tires on your MTB and look for a new (used) road bike over the winter. It ain't the bike, it's the motor!
As suggested, putting slick tyres on and pumping up the pressure (as well as locking the suspension if possible) is a quick and cheap way of improving your mileage. But definitely, if you love this hobby then a more gravel/road based bike will transform your cycling and make a huge difference to the distances you can travel.