How do I increase the "planar reflection probe atlas size"?

Questions & Answers
1

After adding more than 1 mirror to my scene from Game Object->3D-Object->Mirror (which uses planar reflection probe for the reflection)

I get the error:

No more space in the planar reflection probe atlas. To solve this issue, increase the size of the Planar Reflection Probe Atlas in the HDRP settings.
    UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&) (at /home/bokken/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:189)

I’ve tried increasing the setting of “Planar Reflection Atlas size” to a very high resolution (from 512 to 4096) and I still can’t add more than one mirror to my scene.

I’m using Unity Editor version: 2021.3.11f1 LTS
HDRP Version: 12.1.7

2

It turned out that i didn’t really understand HDRP’s settings. To solve the issue i had to change cube map resolution in HDRP Balanced performance tier under Lighting->Reflection->Reflection 2D Atlas size.

3

If you want to add mirror use render texture method.