The meross garage door uses a different capability which is why SmartThings doesn’t present it as an option. I’ve DM’d you a link to an upcoming BETA update to LUM which should allow SmartThings to present that option.
As for the keypad control, sure it can be done. Infact one of the popular apps to control garage doors using keypads is this app: [RELEASE] Lock and Door Synchronizer, synchronize your locks with other locks, deadbolts, doors, switches/relays