I have ~400 contacts, some of which are duplicates. Are there any built in /available methods for deduping my contacts?
I implemented a merge functionality when I maintained the app. Isn’t that available anymore?
One option is to use Thunderbird with the sogo connector
Export everything as a csv file, de-dupe in your favorite spreadsheet application. (Address Book -> Tools -> Export)
Delete and then Re-import. (Address Book -> Tools -> Import)
Cardbook for Thunderbird has such a feature. I use the contacts optimizer Android App which works flawlessly.
FWIW, I finally installed khard on my laptop, and I just merge dupes in khard and then sync with Nextcloud. It doesn’t do the batch process that I really want, but it’s good enough.