I really doubt the proliferation of nuclear/biological weapons in Ukraine. I think that the West is aware of Ukraine's increasingly precarious state, hence the hike in military funding, diplomatic "support" and weapons shipments that have already gone out coupled with the material reality of increasingly desperate rounds of drafting, stagnant fronts and the losses Ukraine has already taken in comparison. Sending nuclear weapons or even capabilities of developing them would be a pretty massive risk for little gain; especially if any of those fall into the hands of enemy forces or are sabotaged by such.

Biological weapons even more so. That is just incredibly unlikely. Biological weapons are the true "world-ender" in terms of actual mortality; there are plenty that will be spared by nuclear weapons. Disease has no care for geographical location, borders or politics. Those things only hinder it ever so slightly. Smallpox or various other engineered diseases could easily end most of humanity on a scale that would make a full-scale nuclear exchange blush.

I don't think there has been a weapon to surpass metal gear yet in terms of deployable field nuclear-weapons. Could be a question for @MarmiteLover123@hexbear.net

All though it really comes down to the fact that the second Ukraine even waves a nuclear weapon I think that will be a genuine red-line moment for Russia.