I think covid might have put a pin in anyone planning to try to take the world using a virus. Two main problems:

1. Once the virus is out in the wild, it is out of anyone's control. It will evolve in whatever direction it will. Maybe it will escape the vaccines developed to keep their side alive. Maybe it will just become less deadly before it kills off enough people to collapse the enemy's base.
2. It looks like our immune systems are pretty good actually and those who get sick might just be the tip of the iceberg while most of the population gets immunity from asymptomatic infection.

These two items work against each other. If you try to make a virus that will infect the entire herd, it might be more likely to also be able to attack you regardless of what vaccines you have. If you try to make a virus that won't be able to escape your vaccine's immunity, then the herd might just develop immunity themselves and the virus dies out after only killing a small portion of the population.

So given that, I don't think a weaponized virus is an effective tool to eliminate enemies with because it's both too risky and too unreliable.