Sub panel is not justified right now.
I read up more, and just for future reference, there is no code problem with mixing 240 and 120 receptacles on a circuit. It's just rare, because 240v 20A receptacles, especially ones whichare not for a dedicated appliance, are rare. Usually 240v appliances are on the list of things that require dedicated circuits.There is an enumerated list of appliances that require dedicated circuits, and lathe is not one of them, nor air compressor etc.
Furthermore 240V receptacles are exempt outright from any GFCI requirements, but 120V receptacles in garages are required to be GFCI.
If I made a MWBC with one leg GFCI/120V and the other one for 240V, it would trip the GFCI whenever the 240V was used due to how GFCI works. The 240V current would "look" like fault current to the GFCI.
I will use up 2 precious slots to make a dedicated 240V circuit for the garage. Oughta have one anyway. Then I will have 2 slots left in the panel, both of which will go the the mini-split AC unit I am installing. Some of the mini-split units are actually 120v, so I might only need 1 slot for the AC.