I have the same issue with excess weight but unike you I can’t shift it. Currently training for a 100 mile road event so most off road rides are between 12 and 50 miles the latter only happens if I can’t bare the thought of riding long on the road. I think once this event is done and dusted I will be riding for pleasure off road and distance will be between 10 and 30 miles.
The road bike will be going up for sale immediately after the event, I hate it.
Hoping to add some running into the mix soon as well as my foot heals, but gym membership is one thing I feel I can’t justify.
Good luck with your continued fitness increase and enjoy.