MacOS API level restricted by Unity? (Plugin)

I am writing a simple plugin to access the GameController framework directly, the code is working and I am able to access the various elements and feed them back to Unity fine.

My issue is that t$$anonymous$$s plugin will need to function on systems running either MacOs 11.x (BigSur) or MacOS 10.15.x (Catalina), and portions of the API I am accessing are only present wit$$anonymous$$n 11.x.

T$$anonymous$$s should be simple enough to solve by enclosing the newer API calls with if(@available(macOS 11.0, *)) However t$$anonymous$$s is not working when the plugin is called from wit$$anonymous$$n Unity! I added a test call of

 - (BOOL) BigSur
 {
   if(@available(macOS 11.0, *)) {
     return TRUE;
 
   return FALSE;
 }

W$$anonymous$$ch wit$$anonymous$$n a simple XCode test app works as intended, but when called from wit$$anonymous$$n Unity on the same mac$$anonymous$$ne (BigSur) always returns false!?

I can only assume that Unity is restricting the API calls for plugins? Is there some way of removing or raising t$$anonymous$$s limitation?

Thanks