http://bugs.winehq.org/show_bug.cgi?id=56391
--- Comment #11 from imaxm memax@gmx.fr --- (In reply to Nikolay Sivov from comment #10)
Module might be loaded, but configure checks for kernel headers. So check that you actually have linux/ntsync.h header installed.
Thanks for the suggestion. The kernel headers (linux-headers-6.14.0-33-generic) were already installed, so that wasn’t the issue. However, the ntsync.h file was missing from the headers. I downloaded the kernel sources from kernel.org, extracted them, and found ntsync.h in the source files. I copied ntsync.h to /usr/include/linux/. Then I reran ./configure and it worked. I was able to build wine with ntsync enabled.
I retested the game and the performance issue has been resolved: loading times are similar to those experienced on Windows. Many thanks to the developers.