It it even possible to roll your own LAN solution any more? The tech giants have become so hostile to anyone who dares to try to control their own data that I never even hear it discussed any more.
I suggest this over an IP camera as you might as well be paranoid about those too. If you need live streaming that can be done with open source software fairly easily.
You would have to spend some time working on hardware, and it'd probably cost more, but technically it's just tedious rather than difficult. There are some projects to do this with the Pi camera already. You could even add object detection with ML quite easily, which is something you pay a lot for with other platforms.
What you miss out on is the level of embedded and mechanical integration that the commercial stuff has. Blink has a two year battery life (replaceable), the housings are IP rated etc.
I was amazed that not a single product in the sub $100 range on Amazon seemed to support direct LAN access. I ended up going with the Wyze cam, which still has that issue, but I'd trust a bit more over the no-name Chinese brands still running 10 year old Linux kernels on their cameras.
From my experience, many cameras won't publicize/document this information, but it's still available/possible for almost every one.
It’s entirely possible to do what you want.