Please excuse me for providing my two cents (plus inflation). Despite having not read a single provided link, it looks like I may have a different perspective based on what I had been reading and experiencing during COVID. It is important to see the big picture and not focus in minutiae.
When SARS-COV-2 was first detected, the medical establishment was concerned by the effects. Perfectly healthy people were hit extremely hard in rare cases, and those with various health disadvantages were in serious danger.
At first, they did not have a clear handle on how COVID spread. So, erring on the side of caution, they treated it like the common cold. We were told about droplets spreading through the air, and how long live strain was detected on various surfaces. ("On metal: 18 hours !!!") It took some time before they realized that COVID did not spread quite that easily. I remember reading that detecting live COVID on surfaces may have indeed been the case, but somehow, it still didn't get anyone sick (at least then).
Nevertheless, they were still concerned for a different reason. At this point, 20 year studies came out on the original SARS. These studies showed that SARS gave most people weaker constitutions and severely affected immune systems. (I remember seeing something like 5x more like to catch colds, or something.)
Anyway, just like the original influenza, the severe strains of COVID died out (when someone dies, they are not a carrier, but when someone has mild symptoms because of a milder strain, they are). We masked up through Beta but when Delta arrived in Israel, RYBs told us not to bother. Delta spread like a cold - masking was useless, and even vaxing didn't stop it, though the heiligeh medical establishment assured us that the vax kept us from getting too sick. By the time Omicron hit, RYBs had us off of vaccines also, saying that the side effects of the vax were (at this point) not worth avoiding COVID.
Did masks, staying 6 feet apart inside with partitions and ventilated rooms, etc, help enough to matter back in the beginning? I don't think anyone can say for sure. There is no way to make a proper scientific experiment, with controls, in an environment that is controlled absolutely. For every anecdote you have one way, I can find another.
Here's one: Sanhedria Murchevet was about 70% non-vaxed, non-masked. Our shul was the only exception - and we lost members who couldn't be bothered, and gained a few who were uncomfortable elsewhere in the neighborhood. We masked religiously (hey, the Rav said), stayed apart from everyone. In our shul we stayed far apart and opened all the windows. I learned at home for summer zman, and in Elul I had a ventilated section of my beis medrash partitioned off with masks and social distancing. When someone was near someone else who tested positive, we stayed home (at first for two weeks - then as tests became widely available, one week with two negatives). Although several members caught COVID, it was always from elsewhere where they had no control over the environment. There was not a single case of spread in the shul. When the vaccine became available, the Rav actually had us wait because what we had been doing appeared to be working. When Beta arrived, though, the Rav told us to get vaccines. No one in my immediate family got COVID until Delta - I know because every cold had us testing constantly, as per the Rav's instructions.
Is the above worth anything? I don't think so. But it sounds nice...
Even though we did all the rules, the very first shiur the Rav gave in public was essentially a long limud zechus for those who didn't. He said it wasn't clear that this hishtadlus is required in order to prevent yourself and others from getting sick. He noted that saying these guidelines helped is not the same thing as saying they helped very much. Since we didn't have enough info, he said it is a good thing to try, but he also said that lav davka we are mechuyav. It seems like he treated it very much with an open mind.
