I mean, on PTL I’ve always heard “either use it the day you get it, or dry it for 3-6 months.” Either approach is fine. Using wet wood, yeah it’ll shrink a bit, but it’ll all shrink about the same amount.

The warping and buckling I don’t think is related to it being wet with treatment— drying would only make the wood shrink up a bit and maybe show some splits and cracks.

Warping and twisting is likely due to the generally poor grade of lumber sold in all big box stores. I’d suggest sniffing around your local independently owned building supply places, and maybe getting something a little beefier. 6x6’s are heavy buggers and might be overkill, but they don’t tend to warp or buckle.

If you think 6x6’s would look silly, you could always go with metal posts and then encase them in cedar 1x.