In a way, China did already have a form of UBI in the past. When I visited China in 1993, almost everyone was part of a 'Unit' that provided all the basic needs, such as housing, heating, schooling, medical treatment, and such. Large units would have their own schools and restaurants. My then mother-in-law received about 200 Yuan as a pension (women retired around 55, if I remember correctly), and that was enough for buying food and clothing. All other things were provided for free by the unit. The luxury item at that time was a (land-line) telephone for which there was a waiting list at the unit. It was all rather basic, but sufficinient. Houses (mostly flats) were assigned by the management of the unit and there was quite a bit of social control. I was told that within the yard (about 200 houses) everyone knew you I was.
I guess, that officially everyone is still part of a unit, but that for many people this is just an adminstrative issue, and a lot of people have a job and/or properties outside the unit.