It's been the case for me as well, no RSR setting for my 6500 EGPU setup ever since 22.3.1. However, what's interesting is that yesterday, after installing the AMD Software Preview Driver May 2022 (which came out the same day as 22.5.1), the RSR toggle showed up in my driver. However, the RSR tutorial somehow wrongly identifies my internal display resolution as 640x480, and the feature didn't make any difference whatsoever when I tested it. Now I'm curious whether they enabled the toggle by mistake or did they actually do something to fix RSR for EGPU setups. If possible, would you try installing that preview driver and see if the feature works with your external monitor setup?