Great question. We know that a large enough volcano eruption can cause a year long winter so I'm curious how much large scale forest fires can compare. Also, assuming regrowth is allowed, the CO2 impact from the burned wood is neutral in the long run.

No. Entirely anecdotal and of my own observance.

I traveled from Ontario to British Columbia two years ago when the forest fires out west were really peaking.

I noticed smoke in the air as far as Winnipeg, and it only got thicker as I approached Vancouver.

Surely all of those white/reflective particles in the upper atmosphere are reflecting the sun's rays.

Also, weather predictions that year where WAY off. Predictions were always much higher than the actual high of the day. I assume this is resultant from historical weather data being a poor source for an altered state weather season.

The smoke covered almost all of north america at some points and it really got much cooler than seasonal averages.

This is anecdotal quantification, but I lived in northern California for a few years and late June would usually be in the 100s or 110s. By August when California catches on fire, it cools down to 90s (when the smoke was blowing our way).

By contrast, when I lived in Texas (no fires), June and July would be in the low 100s, and the first two weeks of August would be 107 - 112.

Back in the early 90s a volcano erupted in the Philippines. In Canada where I grew up, late that summer in August, it was below freezing in the mornings. I had never encountered that before and was a direct result of the volcano.

Is public knowledge than most smoke in wildfires is water. If we see white smoke, is water vapor (mostly).

Unlike volcanoes, any temporary cold effect from clouds would be negated by the permanent destruction of the forest.