Fairly new UK Roadie turned MTB’er here too. Last year i bought a Trek Procaliber hardtail XC when the weather turned good but i no longer wanted to have to do 50 miles of road riding for a good outdoor workout, what with the current state of the driving aggro, incompetence and hate out there on the roads.
So my outdoor rides are now about 30 miles in 2 hours, mostly over fast fireroads and forest trails, with road sections to link up the trail sections. I’ll spend 70% - 80% on trails and it’s fantastic. Not having to worry about cars is great, and being out in the forests and hills is awesome.
One thing i did was do a couple of the “Glorious Gravel” series of rides to get an idea of the great tracks around where you live. Gravel (as a quasi-religion, and on the wrong bikes, rather than just a road surface) is a load of crap if you ask me - Use a hardtail and have just as much fun. As a TR user you’ll be overtaking the gravel riders anyway. 