Thank you @joseph_1979 I found a solution.
For future reference:
- You have to update the firmware of both the NVR and cameras: In my case, the FW of my cameras was 3.0.x, I updated to the v3.1.0.956_22041501 (my camera HW version: IPC_523128M8MP). To update FW of the cameras, you have to do it through NVR, it's not possible to do it anywhere else - docs here: https://support.reolink.com/hc/en-us/articles/900003659286/
- FW of my NVR was 3.0.x, I updated to the v3.3.0.226_23031609 (my NVR HW version: N3MB01)
After all the firmware updates, I have smart detection alarm delay available both in my Reolink Client and app. Also, not only alarm delay, but I can change the sensitivity for smart detection too - for each category separately: PERSON, VEHICLE, PET.
So if you're facing the same issues with your NVR RLN8-410 (N3MB01) with cameras RLC-820A, follow the bullet points, you'll end up having many more features available, helping you to fine-tune alarm detections and prevent false alarms.
