Honestly, I don't think UV return air would work as well as you think. The real solution is increased ventilation rates.
UV bulbs are expensive (and invisible unless you get to poke around a buildings mechanical room.), they need to be replaced typically ~annually (they won't be). If they get dust on them, they don't work as well. Etc. etc.
And here's the issue: To actually deal with high concentration infectious aerosols you need to get that air out of the room ASAP. (i.e. negative pressure rooms) If you can sterilize the return air that's great, but frankly I suspect dilution and air movement is going to be the dominant effect in reducing infection chains.
I think opening up windows is the answer, but that would mean accepting either a loss of climate control, or greatly increased energy costs. (I'd prefer the former, in all but the absolute hottest summer days or the deadliest cold.)
The most interesting phenomenon I noticed was how unquestionably loyal many places were to the mask mandates, yet kept all their windows shut even on totally nice days out.
I was in a gym that required everyone to wear a mask (yes, while working out / on a treadmill / etc), but all the large windows were shut, and nobody seemed to care or notice. No staff, no patrons, nobody. So I walked around and opened all the windows. And this wasn't March 2020. This was like end of 2021.
I'm not claiming to be some pandemic savant, nor getting into a mask debate, but what shocked me was the "group psychosis" on masking at the expense of proven and incredibly easy mitigation efforts like opening windows!
In my house at least I have a UV light in my central HVAC that is supposed to be replaced every five years. Maybe it is different for commercial buildings, but commercial buildings also tend to have professional maintenance.
UV bulbs are expensive (and invisible unless you get to poke around a buildings mechanical room.), they need to be replaced typically ~annually (they won't be). If they get dust on them, they don't work as well. Etc. etc.
And here's the issue: To actually deal with high concentration infectious aerosols you need to get that air out of the room ASAP. (i.e. negative pressure rooms) If you can sterilize the return air that's great, but frankly I suspect dilution and air movement is going to be the dominant effect in reducing infection chains.