
I am not sure if everyone knows this but I did find Meross has a HomeKit compatible garage door opener workaround for Chamberlain/Liftmaster security 3.0 devices.
The short version is you plug the garage door opener into the remote. I took apart the remote like I was going to change the battery, I put the two wires that normally would go on the garage door onto the remote covering the appropriate button and watched on my security camera the door open and close when I opened/closed the door in the Meross app and in the home app. You do need to solder the wires to diagonal (maybe opposite? I only tried diagonal) sides.
I have the liftmaster 6690L and it was able to remotely open it successfully. Since my remote has 3 buttons I should be able to wire up to 3 doors on it. It acts like you are pressing the remote to open the door instead of just triggering the door itself. The only thing you have to watch out for is making sure you wire it to the correct button on the remote and that all the remote buttons are paired to the correct door.
Their guide is at https://www.meross.com/en-gc/mTerminal/FAQ/787.html