Because of your fast mouse speed the mouse skipped over the collision of the virus, so it couldn't detect. I don't know why I didn't thought of the idea to change the color of the viruses before they explode, I guess it was good enough for me. Playing a freezing sound when the mouse gets frozen goes into the same group as the changing color before exploding, it was good enough. But I will note that for my future projects!
The bugs/viruses should look out of place, they are on an "another dimension" you could say, but maybe I got carried away trying to make that feeling...
Also, about the font stylistics, I was too lazy to import a font into godot (I am very lazy), so I just used the system font. But I did use the Segoe UI font while creating the upgrades.
Also, no you did not reach the boss. That sequence happens when you loose. I know I've made it a bit confusing and up-in-your-face, but that was the best idea on how to indicate that you lost. But retrying and getting to the boss is absolutely worth it! I absolutely love the boss design and what he does. But note that the boss only appears in the desktop downloadable version. I had no time making the boss work with the browser and it wouldn't be so thrilling.