As Computer Base highlights, enabling Turbo Game Mode in the BIOS disables a processor’s second core complex die (CCD) / chiplet when applicable and also deactivates simultaneous multi-threading (SMT). For CPUs with a single CCD, the toggle will simply turn off SMT.
Nice. Does that mean I can take my 1980s computer case back off the shelve, and finally get to use a Turbo button again?