Both China and the USSR conducted mass collectivation, land reform, commune models among other things to move away from capitalism to a communist model of public ownership. They even killed dissidents, violently oppressed public protests and starved their own people in the attempt.

And it was a massive failure.

It's a "no true Scotsman" fallacy because as long as attempts at moving to a communism model fail, supporters will just say "that wasn't true communism" ignoring the fact that if you can't actually create a functioning communist system that's indicative of failure of the model itself.

Like I said, everything that you have describe was not communism - it was a particular recipe for supposedly building it. And yes, that recipe was a massive failure, and few people on the left believe that it could have ever been anything but.

But here we're talking about communism naturally arising out of technological post-scarcity. What does that have to do with Soviet model of "public" (actually, state) ownership, or killing dissidents, or violently oppressing anyone?