Thank you,
Alright, for anyone else who is troubleshooting.
My Meross msg200 garage door opener was purchase in Aug 2021 and is a pre/non-homekit version. I can see firmware version 2.1.3 in Hubitat (and I also see hardware version 2.0.0 when I look in HA). I do not have any available updates when I look in the app, so it appears 2.1.3 is the current version for my 2.0.0 for my hardware.
What I just tried based on pjam73's earlier comment was to change all references of the version in the drivers code to 213 (the 0s at the end of line 67, 98; and anywhere there was a value of 323, I changed it to 213.) That solved my issues, and my opener is now working as expected.