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.
It didn't close so much as rebrand as the United States Army Medical Research Institute of Infectious Diseases.
I don't think the US has labs abroad but other countries such as the UK and Russia have mucked around with bioweapons research in the past. Probably China too as it has a general policy to keep up with the opposition.
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.