I ran into Droidcam during the pandemic when I needed a webcam and you could not find a decent one anywhere (or it would cost an arm and a leg). It works over USB or network, and it can connect two ways (phone can connect to PC or PC can connect to phone) so you can connect it over Internet or over VPN (like Tailscale). The PC app can work without a GUI so you can install the app for example on an old phone, connect it to power and use it as a surveillance camera too.
I ran into Droidcam during the pandemic when I needed a webcam and you could not find a decent one anywhere (or it would cost an arm and a leg). It works over USB or network, and it can connect two ways (phone can connect to PC or PC can connect to phone) so you can connect it over Internet or over VPN (like Tailscale). The PC app can work without a GUI so you can install the app for example on an old phone, connect it to power and use it as a surveillance camera too.