I know Wyze and Tapo's security cameras will still cache event recordings onto the MicroSD without a paid subscription. The former will just continuously overwrite fifo style when storage exceeds the card's capacity; should be trivial to recover if they didn't implement CMD32, 33, 38 specifications correctly (or the SD is too old to support those commands).

Those aren’t really local and they still ping the cloud even if you choose not to use their cloud storage. If you want to truly have local setup, do so by having all the CCTV system on a separate vlan that can’t access the internet, but the NVR is connected to you through vpn, that way only you can access it. Note: thingino is an open source firmware for cameras too, that being said, it lacks many features that I won’t recommend it, better is just using stock but blocked from internet.