How to remove duplicate contacts?

Hello and thank you for NC,
I’m using NC
yesterday I was looking at the “contact backup” section in Nextcloud, and it suddenly reimported all my contacts. I did it again to check why it happened, and now I have 3x of all my contacts.

I was looking if it was possible to make it from a thirty part client, like Thunderbird. Unfortunately this plugin is not compatible with the last Thunderbird version.

Is there an easy way to get rid of duplicates?

Thank you.

This feature request seems to be still open (2019)

Merge duplicate contacts [$70] · Issue #70 · nextcloud/contacts · GitHub

also here
[Suggestion] deduping contacts - #4 by lars-becker

Thank you. I’ve seen these topics, but I hoped that there was a workaround.