UI: Disable multitrack video settings on non-win32 platforms

UI/window-basic-settings.cpp

@@ -6325,6 +6325,10 @@ void OBSBasicSettings::UpdateMultitrackVideo()
 			ui->enableMultitrackVideo->setChecked(false);
 	}
 
+#ifndef _WIN32
+	available = available && MultitrackVideoDeveloperModeEnabled();
+#endif
+
 	if (IsCustomService())
 		available = available && MultitrackVideoDeveloperModeEnabled();