Coleman AT200-B won’t start. Please help?

[RidgeRacer]

I have this Coleman AT200-B that won’t start. I believe they run GY6 engines. The initial issue was that the alarm/kill remote was faulty. Turning the key would set the alarm off. They unplugged it while trying to get the atv started. It would want to start but then quickly stall..
I replaced the alarm/remote and that works as it should. As I worked my way through the ignition system, from battery to engine, the engine no longer turns over. It sounds like the starter is moving but nothing is engaging.
I have replaced: battery, starter solenoid, starter, cdi, ignition coil, spark plug, stator magneto, and most recently the starter drive clutch.
What I noticed while taking it out of the garage is, it rolls freely in Drive, as if it’s in Neutral. Reverse feels good. I did attempt to push start it, nothing engages. Again, probably due to the free moving Drive gear.
I have exhausted all my knowledge of small engines. Any idea what the trouble might be?

[RidgeRacer]

https://drive.google.com/file/d/1UCD...w?usp=drivesdk video of attempting to start it.