I have some amcrest cameras that are on PoE, save data to an SD card and aren't connected to any amcrest cloud services. They work great. They have a viewer app that I remote into my network to review, but has no cloud connectivity outside of that. I have the switch and modem (and router) on a battery backup for the rare times I lose power.
As far as I can tell this is a minimally viable passably secure system that "just works", requires no other hardware, and has local storage.
A few more steps such as a (edit: dedicated) hard drive backup, nvr and so on would be great, but my needs are currently met.
This or something like this might be of interest for someone trying to move away from highly cloud connected subscription services but who aren't ready for a more "hobbyist" setup.
It took me longer to research a quality sd card (so many fucking acronyms) than it did to install and test my 4 camera system.