Hey Gareth,
I recently picked up a Reolink POE doorbell camera and integrated it into Camect and Home Assistant. My Camect hub and cameras, including the doorbell, are on a separate VLAN with strict rules to prevent the cameras from accessing the internet (and thus not self-updating) but allowing Camect access to the internet and desktop VLANs.
The doorbell supports RTSP (once enabled in the web interface) for complete offline use. I did not set up the app or their cloud service. The included wireless chime still works. This is a bit more advanced setup but works great if you wish to be fully offline in a secluded VLAN or similar environment. I have yet to install the doorbell, however it has been running for a couple weeks on my desk with no issues. The only caveat is that you have to have a wired network connection at your doorbell location. The POE model does not support wired chimes either, only the included wireless chime. I have access to fish CAT6 to the doorbell location in my home but that isn't always possible.
Hope this helps! Happy to answer any further questions.
Mitch