the NVR and SADP doesn’t recognise the camera.
Presuming the camera isn't connected to an NVR PoE port.
If it was - SADP will only see it when the PC is on the same network, such as when connected to an unused NVR PoE port.
Worth trying also is to power the camera from a 12v supply if it's currently on PoE.
Sometimes that works when there has been corrosion damage on the RJ45 connection - which is usually obvious on inspection.
The cables can be replaced if it's thought worth the effort.
Or is it a case of just replacing the camera?
Probably, depending on what a little fault-finding shows up.
Which would be an opportunity to see what later generation cameras are capable of!
Things have moved on so much.