What is the ambient temperature when this happened?

Jim

A simple compression and leak-down test will confirm rings or valves. They
are "relatively" inexpensive to do...only take it to a Porsche mechanic!

You are right, it might be burning oil.  If you rarely drive it, and then
around Taipei (you did say you were in Taipei, right?) then you may have
built up some varnish on the pistons and the rings may be stuck (probably
the lower, "oil" ring).  As I recall the Taipei area, there really is
nowhere where you can get the car up to speed and keep it there for a long
time (an hour or so), and so the build up of varnish from the engine
combustion products is more likely.  I have fixed this situation once (but
not on a porsche) by using an oil additive that is supposed to clean the
engine inside.  You may wish to try this approach.   Or, you may just ignore
it - I dn't think it will hurt anything (except the image of the car).

An interesting experiment is to hold a rag over the exhaust to catch some of
the smoke - if it's oil, you will see and smell oil on the rag. If it's
something else, it won't smell like oil.   I don't know your exact car, I
have seen white smoke (on a mustang and on other such cars) when the
transmission modulator (on an automatic transmission) fails.  I presume your
car has a manual transmission, but it it's automatic, that's a possibility
also.

Also, what type of oil do you use? synthetic or regular