Russia ... doing this kind of thing all the time.
Literally, since like 1946.
Conversely, what is different, is that Chinese troops are training with Belarus troops near Ukraine & Poland borders, practicing seizing an airport.
So, it is all likely just widespread cooperative training exercises (we do them all the time with NATO member nations), but there is no denying that it is worthy of note that China & Russia are working together.
For all of the "Trump loves Putin" or "Biden is in Xi's pocket" talk... the bigger takeaway needs to be that those two are working together and we shouldn't be liking EITHER ONE.