Fort Detrick and all other US bio weapons ceased research in offensive bioweapons in 1969. One reason is that bioweapons can't be controlled, as evidenced by the failure thus far to control this virus. So no, it's not likely that there are undisclosed US bio weapons research sites; that's just propaganda.

While I don't trust the CCP a bit, I also doubt that China is pursuing bioweapons research, for the same reason: a bioweapon is too likely to backfire. If the covid-2 virus came from a lab in Wuhan, it's not because they were pursuing it as a potential bioweapon, it's because they--and others--wanted to understand how to protect against it.