This is a pretty interesting claim...I have a few C110 and C200 that work just fine offline after null routing them.

You may need to enable RTSP (https://www.tp-link.com/us/support/faq/2680/) to get a feed off them directly, it works fine in Frigate and any other viewer that can consume RTSP.

I am not defending TP-Link, but it's a pretty big claim for you to say their devices don't work offline and will immediately power down, without any supporting technical evidence.

This trend worries me too. Losing basic local functionality just because the internet is down feels like a step backward.

I think a starting point to avoid such things even if one does not use Zoneminder would be to look at their hardware compatibility lists [1] and ask on their forums [2] to find stand-alone cameras and keep them on an isolated network using a layer-7 proxy such as HAproxy [3] to reach your management interfaces so they do not have a gateway but you can still access your devices.

The forums of all the assorted open source NVR's would also be a good place to share your findings. Zoneminder, Shinobi, Frigate, etc... I mentioned Zoneminder as they are used by a number of corporations and requiring an outbound connection to a 3rd party would be a show stopper for many of them so this topic should be a shared concern.

[1] - https://wiki.zoneminder.com/Hardware_Compatibility_List#IP_C...

[2] - https://forums.zoneminder.com/

[3] - https://www.haproxy.org/

it probably checks if the firmware needs to be updated.