The photo basically shows what it is:
A bolted ring is a common feature on spaceships and rockets, as it provides a very strong seal with no corners. This one is reminiscent of another UFO that turned out to be a bit of a Chinese rocket:
https://www.metabunk.org/explained-...crater-space-junk-part-of-rocket-motor.t8252/
Another picture from that case should ring some bells with the current one:
Notice here the criss-crossing fibers, just like in the Russian case.
So what we have here looks like a human made carbon-fiber composite fuel tank - a high pressure container for liquid gas like hydrogen or oxygen. This is probably the top (i.e. the end opposite the nozzle)