You seem to be glossing over the difference between UV-C and UV-A/B.

UV-C (the one used for sterilization - splits the thymine bond in DNA/RNA) is higher frequency (shorter wavelength) than B and, although it is emitted by the sun, does not make its way through the atmosphere to ground level- which both A and B do.

Back pre-pandemic, there was some interesting work being done with far-UVC (up at the shortest wavelengths of UV-C). The advantage of it being that, although it still degraded thymine, it could not penetrate the outer (dead skin cells) layer of the skin of the layer of tears over the cornea. I suspect they may have run into issues economically producing emitters - there'd be a huge advantage in being able to safely bathe large public spaces (e.g. train stations) in UV and so quickly degrade any airborne pathogen.

Lacking far UV-C (or at least a safety certification for use in public), UV-C in general can be used as a biocide against airborne microorganisms - you just have to protect people from it. For instance, the bil lab I did some work in when I was in high school (late 60s) had multiple wall mounted devices near the ceiling. Being the person I still am, I took one apart (while powered off). It consisted of a sheet metal box baffled to let air through but block direct light rays, a fluorescent lamp, and a fan to move air through, past the lamp. They were near the ceiling, and the baffles let indirect light out upward, towards that ceiling.

The point of those boxes was to prevent contamination of the petri dishes at lab bench height - but they'd work for any airborne microorganism.

I built a small one for at home use when the pandemic started, based around a couple of UV-V LED emitters (high-ish, but not quite 'far') sold for water treatment systems and a couple of computer fans. It might have been important if one of us had come down with the disease. Thankfully, I never had to test that out...