If you race road or do big road kms then you’ll have the legs for MTB.
Faster guys will call out if they want to pass, don’t put yourself out for them unless it works out the best for everyone, especially you.
Climbs can be technical, a good line & low(er) speed can be cashed in to save your legs for bigger battles.
MTB can be pretty intense physically & mentally. You’ll be called on to crank, brake, turn, balance, look ahead & dodge all at the same time in places.
See the line, not the obstacle. Momentum is your friend. You’ll be surprised what a MTB is capable of riding over & through. You don’t need to grip all the time, just in the key places, the rest can let slide/drift/see air, it’s all a fluid & loving thing…
Just a bike & a place to ride.