This is certainly an impossibility, because China monitors in and out going research, there would never had been an American bioweapons research in China, unless it was a collaboration between both countries. Which is not likely at all.
If you want to be conspirational one can guess that US did release a bioweapon, but China turned it around (the widespread covid variant targeted obese and thrombogenic people much harder, which is the opposite of Asians).
I lean more towards a natural disease where the first known super spreader event was in Wuhan, but it likely started somewhere else first, since it was easy to contain it in China. If there were foul play in bioweapons from either US or China, they can post documents online to expose the other side.
However, if a high level US decision was made to "encourage" people (especially ones working for US regime such as soldiers) known to be sick in a natural seasonal diseases US CDC is incompetent/willfully concealing to travel to a Chinese transport hub during the holidays, there might not be a plausible paper trail for China to leak.
Two years ago Canada's Conservative party made a big fuss about demanding to know what happened at Winnipeg lab, where two Chinese virus researchers were arrested by CSIS for sending totally not COVID samples to China in summer of 2019. The ruling Liberals then invited them to a classified briefing, and the Conservatives stopped all mention of it ever since.
The sample sent to China from Winnipeg in the summer of 2019 was definitely COVID, it was sent to Winnipeg by Harvard's Charles Lieber who was also arrested for it, and the recipient of the samples in China was eventually given Hero of the Republic medal. So China definitely knew about the weapon before 2020, hence the immediate BSL4 order after first sequencing in Wuhan and finding it's the same virus as the summer sample.
The way I see it the sequence of event was: concept for the attack was formed in 2018 around time of trade war, Crimson Contagion exercise was carried out late 2018/ early 2019 that naturally showed US emerging with least loses, order to deploy was then given, the sample was then either deliberately or accidentally leaked from Fort Detricks in 2019 as cover, Lieber either due to conscience or believing it as a leak sent samples to colleagues in Winnipeg to study, those colleagues then immediately sent it to their contacts in China.
There are a large body of evidence pointing to pre-spread in the US in 2019, if Crimson Contagion exercise didn't happen it could be explained by a leak, but the exercise did happen and its content was the exact scenario that unfolded a year later.
IMO it's likely the eventual variant that spread in the west was China's counter-attack rather than a natural mutation from the original variant tailored for China. Early news reports from the US paid unusual attention to viral mutation in quarantined China arrivals, and US swong from let-it-spread to max-lockdown after detection of the new variant.
In either case I find it funny how Americans (and Canadians) have themselves converged on acknowledging COVID is their creation, but make up elaborate conspiracies to explain how it ended up in China, as opposed to far more obvious and simple explanations.
