A DESCRIPTION OF THE PROBLEM :
The size of the returned symbol is 0.
In order to access the POSIX variable timezone of time.h one needs a extra conversation to MemoryAddress.

MemorySegment timezone = SymbolLookup.lookup("timezone").get()
timezone.address().get(ValueLayout.JAVA_LONG, 0)

but having a size

MemorySegment timezone = SymbolLookup.lookup("timezone", 8).get()
timezone.get(ValueLayout.JAVA_LONG, 0)

This would preserve the MemorySession of the SymbolLookup instance and eliminate the transformation to MemoryAddress.
Storing only the MemoryAddress would complete eliminate the MemorySession, this could lead to other problems.