I disassembled it on the first day. There’s a bolt that holds the rear triangle together. Definitely a proprietary setup. Believe me this one has been through trial and error (hence the suspension “backrest”) if I had used a regular backrest it would have buckled eventually. As it is it devours...
To be honest I find phreaking the newer big box store bikes (don’t they all come in boxes?) to be a bit easier. Also I don’t miss selling or giving away those at times because I can usually find another if I look hard enough.