Chamber length and patterns

It can yes, because there's more of a "jump" between the shot and wad and the actual barrel.

In theory it should be able to affect pattern, but I have not been able to detect any measurable difference real world.

With modern polymer wads the last few inches of the barrel have a far greater impact on the pattern than the first few. I have shot lots of 2-3/4 shells through my 3.5 BPS without issues.

Never shot a 3.5" chamber. I know there is very little difference, if any at all, between 3" and 2 3/4" chambers. It would be a hard thing to actually test without starting with a 2 3/4 inch and reaming to 3" since you would be using different guns otherwise.

Every shotgun patterns uniquely. It’s hard to correlate chamber length to pattern. My Mossberg 835 is overbored, and throws excellent patterns with everything from 2 3/4” trap loads thru 3 1/2 magblends. When I got my 870 Special Field 20 ga I took 9 different loads to the pattern board spent 4 hours to determine it loved Federal 1 oz. 6 shot field loads. My Grouse load for 30+ years, those 4 hours have put countless birds in the game bag.