Do we have any evidence that the UK strain is significant in France, Italy, and Belgium as of yet?
I'm not sure about how many cases can be linked to it outside of the UK, but supposedly, it was the primary driver of cases in the UK, and it's all over Europe now. So, it seems plausible that it was or is an important driver of cases in Europe and in other areas as well.
https://www.bbc.com/...europe-55449528
And did maskless indoor private gathers suddenly take a spike in mid September (ish)?
Look, I'm certain that as we got into winter proper people being indoors more has increased the transmission rate. It's only logical. But I question whether that was an effect earlier in the September/October time frame. In fact, in my area I see more people outside in late September/early October because it's no longer oppressively hot and the weather is more conducive to being outside.
Maybe indoor humidity changed enough to lead to a condition more conducive to the spread of the virus among the maskless, even if the total number of private gatherings was somewhat less.
People just have to bit the bullet and wear masks around other households or avoid them altogether until this pandemic is over. This is logic 101, not rocket science.
What I see is a tendency from the pro-mask crowd to explain away every suggestion that masks might not work as well as they have suggested. It's the new strain, poorly ventilated areas, people aren't wearing them at home in family gatherings, their masks aren't that good, the list goes on and on. Everything but to consider that mask might not work as well as they'd hoped. I think that betrays an emotional attachment to a favored theory.
Look at the totality of the evidence. Mask mandates generally started to come into play in late March through late April. And dutifully we watched as infection rates decreased and we said "Aha! The masks are working!". But, as we slipped from summer into early fall and infection rates started to rise again, and more people were wearing masks than earlier in the year (because even as those initial mandates were imposed it was still very difficult to get masks unless you were making your own) the same people have been reluctant to question to what extent these masks have been helpful. I think it is very difficult to contend that masks caused the decreases in the spring in light of what happened in the fall. And look at those graphs of death rates between countries like Sweden which is has little in the way of mandated social distancing and masking and other Western European countries that do - you don't see a great deal of difference.
Masks probably help to some extent, but I don't think they are a panacea.
Since you still seem think that there's something to the seasonality idea, why don't you present some evidence that's a little more convincing? It shouldn't be that hard to find some charts with temp and humidity data.
You say Sweden, I say Norway and Finland (where masks are recommended). You're still going to get cases and deaths with masks but a lot less than what otherwise would be the case.
For now, the fact remains that there's more evidence that masks (if they're actually worn) are a much more important factor than seasonality. Maybe they don't work that well with more contagious variants, and if that's the case everyone will just have to wear respirators or endure lockdowns.
A more interesting and important discussion to have is about respirators. Why hasn't any expert recommended wearing respirators instead of cloth masks? Has respirator manufacturing capacity expanded enough in the many months since the start of the pandemic? If not, why not?