I use TP Link C100 cameras in local network mode and a Reolink doorbell in a similar manner. Standard RTSP feeds and an internal mini web server, plus plenty of privacy controls.

Both of these products are pretty cheap considering their configurability — they do both provide the option to do the whole cloud subscription thing, but work fine for me without it. I have Home Assistant on the back end to manage live streams, but find I usually just read data off the internal SD card instead.