Do you have both, EndNote and Mendely installed on your system?
If yes, deactivate Mendeley in the Word coms and you will succeed. Here is the macro that I use:
Sub TurnOffMendeley()
'
' Toggle Mendeley temporarily
'
' © Christian Wolkersdorfer c.wolke@web.de
'
' 2021-06-01 initial version
' 2021-06-20 mendeley version will now be detected
'
' ensure Mendeley version is correct
'
wordStartupPath = Environ("appdata") & "\Microsoft\Word\STARTUP\"
menVersion = Dir(wordStartupPath & "Mendeley-*.dotm")
menPath = wordStartupPath & menVersion
AddIns(menPath).Installed = _
Not (AddIns(menPath).Installed)
End Sub
edit: code optimized for other Mendeley versions