Remember the NVR needs to process all the incoming camera streams to record them which can be around 3-4MB/s each on a 4k camera (double that if using 8K). So yes the UCK G2 Plus has Protect but hardware wise it's really only good for recording like maybe 3-4 cameras so you need to upgrade if you want more capability. The UNVR will handle up to maybe 12-14 cameras and the UNVR Pro will do up to around 20-22 cameras (beyond that you need to move to the ENVR which can go to around 70 cameras). So in my case I'm just using the UCK G2 Plus as a controller for everything on my Unifi system. It's nice because it's always on (no need for a server or anyting like that) and allows me to make changes, view all the switches/APs/etc so it's really the best way to do that unless you're using a Unifi gateway which I don't.
If you want to play around with the capabilities then you can go to the Unifi store, select the device and click on the "capacity calculator" tab near the bottom:
Compact UniFi Console that connects directly to the Site Manager at https://unifi.ui.com/ for powerful, multi-application site management.
store.ui.com
A video recorder with (4) 2.5/3.5" HDD bays that can support up to 30 days of storage for (18) 4K cameras or (60) Full HD cameras.
store.ui.com
A 2U-sized video recorder with (7) 2.5/3.5" HDD bays that can provide up to 60 days of storage for (24) 4K cameras or (70) Full HD cameras.
store.ui.com
3U NVR with (16) 2.5/3.5” drive bays, supporting up to (70) 4K cameras or (210) Full HD cameras.
store.ui.com