See some of the previous threads for discussion of this question (and why it isn’t going to happen – at least not in a form that anyone has proposed so far):
https://forum.inaturalist.org/t/revisiting-duplication-of-another-users-observation/56844
https://forum.inaturalist.org/t/duplicate-observation-of-another-user/6292
https://forum.inaturalist.org/t/add-a-request-duplication-button/52215/8
There might potentially be other ways to “salvage” the additional data connected with other organisms in observations (for example, creating a more robust, easily searchable version of observation fields with a community review process for “additional associated organisms” that would be linked to an observation but not separate observations themselves), but duplicating observations of another user is something a lot of us would be unhappy about.