This may not actually be true according to Politifact, as it's likely a lie used to justify invasion (much as NATO is cockblocking Russia from raping Ukraine.)
Ukraine, US Biolabs, and an Ongoing Russian Disinformation Campaign
https://www.snopes.com/news/2022/02/24/ ... ne-russia/
Claim: 7 of 11 locations were missile targeted by Russia (and presumably have exposed the environment with whatever they were testing.)
Map of locations and info on bio threat mitigation
https://meaww.com/putin-bioweapons-labs ... ry-experts
Pentagon Biolab in Ukraine Exposed Performing Biological Experiments on Local Soldiers
https://www.planet-today.com/2022/02/pe ... K-i8Ftysbk
It might be to experiment on bioterrorism and how to counter-act it, though it does look suspicious. The US is known to allow experiments on foreign soil and the reason is it has tremendous risks involved with it.
Biological Threat Reduction Program
https://ua.usembassy.gov/embassy/kyiv/s ... K-i8Ftysbk
A lot of the reasons for Putin invading are probably not being revealed to the public. Also, the more desperation made of any diplomacy will have significant repercussions if, out of desperation Putin sees no consequences for going thermonuclear instead of thermobaric.
And again, if such a thing were true and were classified, wouldn't such facts be kept secret from the public if they didn't know how to interpret it?