For personal study
Apply the overlaycamera's viewportrect and set the renderscale to 1
Note: It has not been tested for stability and performance.
Update
23.05.10 - update URP(12.1.10) / unity 2021.3.22f
20.11.07 - forwardrender.cs, universalRenderPipeline.cs change
20.11.08 - Test Done(OverlayCamera Viewport,only BaseCamera render scale)