Originally Posted by
fishboat
You do know that sizing a road bike and sizing a mtb are different? i.e. if you ride a 21" road bike, you won't be riding a 21 or 22" mtb..
The OP is looking for advice converting a MTB to gravel and CX use, not necessarily for singletrack. So far the advice provided is to pay attention to TT lengths to avoid getting stretched out, and that stack heights might be short. Gravel and CX fit are likely not too far from a road bike fit.