There's plenty of research on it. There already was before the Year That Shall Not Be Named. Two of the most common "sides" of the conversation both have points.
Regular masks do limit exposure, primarily for the person not wearing the mask. Masks mostly help other people, not the wearer. The barrier to exposure they provide is also somewhat pointless in many situations. They tend to make a difference if two people are at a certain distance from each other, or more importantly, are not around each other for very long. Like your financial investments, time is the most important factor in viral load transfer.
Suppose a guy breathes in your vicinity for 30 seconds. Then suppose that's enough to transfer you a viral load with no masks. It may be the case that had he worn a mask, you would've made it out unscathed. If that same guy breathes in your vicinity for 2-3 minutes, it may be that the extra barrier of the mask is overcome and you get sick anyway. In that case, the mask 1) limited exposure, and 2) didn't matter. Not mutually exclusive.
One's severity of illness correlates to amount of viral load they take in, though people tend to think of viruses in binary terms...."I got sick," or "I didn't get sick." If a guy shedding viral particles breathes on you at a distance, you might get sick, but maybe just a 3 on some arbitrary scale. If he'd breathed in your face for a couple minutes straight, you could get sick at a 10, with much worse symptoms, for a longer period of time. In that regard, masks arguably help at all times, since the viral load transfer is always less with a mask than without. When people say masks are ineffective, they may mean somebody got sick anyway, without factoring in that the person may have gotten even more sick if there were no mask.
But your severity of illness also correlates to what your body does with the virus once it's inside. So it's not all just the number of viral microbes you inhale. I seem to be immune to the flu, no matter how many people cough or sneeze on me. This is anecdotal, but I consider the evidence pretty strong at this point. Some people's immune system kicks back a virus, sometimes completely, but also partially, and therein lies the counterfactuals that are so hard to pinpoint....it's not always obvious how much better/worse off someone would've if there had been a mask/not been a mask. otoh, Covid-19, I am highly susceptible to. I don't tend to get terribly sick from it, but even just a tiny exposure and I'm going to come down with it.
