Can not add-in endnote

That message is normally produced by EndNote, not Word. The registry change may have disabled or removed the Cite While You Write registration, but I would not edit the registry again without knowing exactly what Microsoft Support changed.

First, check whether Word disabled the add-in:

1. Open Word > File > Options > Add-ins.
2. At the bottom, select Disabled Items and click Go. Enable EndNote if it is listed.
3. Change the list to COM Add-ins and click Go.
4. Check EndNote Cite While You Write, then restart Word.

If EndNote is not listed, reinstall that component:

1. Close Word and Outlook completely.
2. Open Control Panel > Programs and Features.
3. Select EndNote and choose Change or Modify.
4. Make sure Cite While You Write for Microsoft Word is selected.
5. Complete the repair and restart Windows.

Next, open Word > File > Account > About Word and note the Word version, build number and whether it is 32-bit, 64-bit or ARM. A very new Insider build, ARM version or mismatched Office installation may not be supported by the current EndNote add-in even when EndNote itself is up to date.

If the unsupported message remains, give those details to EndNote support and ask them to confirm compatibility. If the add-in is missing from Word after reinstalling it, run an Office Quick Repair under Settings > Apps > Installed apps > Microsoft Office > Modify. Reinstalling the add-in is safer than trying to recreate its registry entries manually.