Would you be able to setup a simplified repro in the Playground (just the starter scene with a DOF post process and taking a screenshot with CreateScreenshotUsingRenderTargetAsync)? That would help debugging the problem.
However, this does not work in WebGPU because it seems the size of the canvas can’t be changed anytime we want (don’t know if it’s something expected or a bug from Chrome that will be fixed when WebGPU is live)… Pinging @sebavan in case he has some ideas.