put forward a narrative that COVID-19, either overtly or through their sub rosa information warfare channels, was created by the US in a Ukrainian lab

There were propaganda pieces about that in Hungary 1-2 days after the start of the war. This theory already exists and unfortunately, I know people who actually believe it. It's madness.

Also, Russians like to test the waters with their narratives(the Hungarian government learned that from Russia too). They drop a lot of theories, measure the effect and conduct tons of polls and they will go with what works. Obviously, there are big groups where this theory is doing well, but I do not think this would work well on a larger scale because if it would, this would be used much more.