Keeshare is a feature for Keepass (plugin for the original, build-in function for keepassxc), that allows secure sharing of groups between databases (and usually different users) via "share" file.
This is just a zip file with a kdbx file and a signature from origin.

More information:
https://github.com/keepassxreboot/keepassxc/blob/develop/docs/QUICKSTART.md#using-sharing

Personally, I'd be satisfied with the minimal implementation of the recieving end:
Checking the share file (e.g. every time the database is opened) and importing the key groups inside if the certificate is known.