I’m going over all my entity_IDs as I had different approaches to naming conventions. I noticed some entity_IDs with status “Unavailable”. They are related to ESPHome entity_IDs I no longer use.
I tried to restart HA to see whether this takes care of this but they remain in the list of entity_IDs.
Do I have to edit a registry or do something else manually to remove unavailable entity_IDs. While they don’t do any harm it makes the whole listing bigger than it needs to be.
There is a easier method than editing the entity registry. Just remove the esphome devices from integrations which used to have these unavailable entities associated to and restart HA. This will remove the unavailable entities, then you can add the deleted entites again to get the present available entities back in HA.
hmm. That’s not what I see. Going to ESPHome there are no nodes at present. I have restarted Home Assistant and going back to entities I still see all those unavailable (and some restored) entities. Note that while most of the unavailable entities are from ESPHome there are non-ESPHome ones as well.
In that case you should delete the unavailable entities from the entity registry. Go to the /config/.storage which is a hidden folder inside the config folder. In .storage folder you can find the core.entity_registry file. Open it in node pad or any code editing software and delete the entities from it.
I think there is some confusion here.
You need to delete the ESPHome integrations from the Configuration /
Integrations menu, not the ESPHome addon web page.
The addon only creates and edits ESPHome nodes. It has nothing to do with Home Assistant communicating with the nodes. You can stop or remove the addon entirely and the Home Assistant ESPHome integration will still happily communicate with the nodes.
Ok great, that worked, thanks 
So now I have only 1 unavailable entity from the Tasmota integration which I can’t delete from the pop-up in Configuration / Entities. Taking the cue from what I’ve done to ESPHome I probably could get rid of it by removing Tasmota from Confguration / Integrations. However I have 167 entities and hate to have to recreate all these. How can I safely remove this one?
If this has been discovered via mqtt the easiest way is to use MQTT Explorer to find and delete the retained discovery message for this device from the mqtt broker. Then restart Home Assistant.
This was discovered via the Tasmota integration. This device ran 9.x and became available under the configuration / devices listing once I changed to native discovery (i.e. SetOption19 0)