Check coolant level & compression. Coolant loss could be into the cylinder through a blown head gasket. You would also see overheating, & evidence of combustion gas in the coolant (maybe you'd see soot and or bubbles in there. If the coolant were fizzy, nasty & black, that'd be my guess). If the gasket were just blown into the coolant jacket, you wouldn't see significant coolant in the oil- just contamination from blowby.

If you adjust your valves & do a compression test, 1 cylinder well below the others would indicate a problem w/ that cylinder- the ring, piston or head sealing that cylinder.

If the smoke condenses, that would tell you what it is- water, fuel or oil. If it's fuel, it could be poorly atomized fuel (bad injector), or well atomized fuel that isn't compressed enough to ignite (bad compression).

I would drain coolant & replace, adjust valves, warm it up & do a compression test, look at the injectors when you pull them.