As pointed out here, HDR is absent from LrC for both Nik 5 and Nik 6 versions…even though they are visible and active according to LrC’s module manager:
Update: Copied the plugins from the respective folders in /Users/…/Library/… to /Library/ - but it did not help. Plugins showed up in the module manager, but not in the menu.
All of the above with LrC 12.5 on macOS Monterey (latest) on iMac 2019…and the expected stuff is present as we can see in EasyFind: