Here a new binding available in OH3 official distribution.
The Remote openHAB binding allows to communicate with remote openHAB servers. The communication is bidirectional. The binding on the local server listens to any item state updates on the remote server and updates accordingly the linked channel on the local server. It transfers any item command from the local server to the remote server. It can map any remote thing to a local thing. Through this mapping, in your rules (local server), you can take actions based upon status updates or status changes generated by remote things and you can take actions based upon trigger events generated by the trigger channels defined in the remote thing.
One use of this binding is to distribute your home automation system on multiple openHAB servers.
Another use is for users to interact with older versions of openHAB that may support old openHAB v1 bindings that were not migrated to openHAB v2 or openHAB v3. They can keep an openHAB v2 server to run their old openHAB v1 bindings and setup a new openHAB v3 server for everything else. The Remote openHAB binding installed on the openHAB v3 server will then allow to use the openHAB v1 bindings through communication with the openHAB v2 server.
A third usage is for users that would like to keep unchanged an existing openHAB v2 server but would like to use the new UI from openHAB v3; they can simply setup a new openHAB v3 server with the Remote openHAB binding linked to their openHAB v2 server.