It does within margin of error. Try it with a previous version of UE5 where you can still use setres without it bugging out.
Yeah, you use a simple equation to calculate the % you need. Just get the display resolution and then the equation is: resolutionscale = 100*(target resolution/display resolution). Want to go from 1440p to 1080p? (1080/1440)*100=75. Want 4k on a 1440p? (2160/1440)*100=150 and so on.
Most modern DX12/Vulkan games all do this under the hood, even when they give you resolution options in the settings. Exclusive fullscreen for DX12 really isn’t a thing any more and if you do force it by disabling FSO/MPO and messing with the present methods, it can have some performance drawbacks with modern drivers and builds of Windows. So there’s no need to actually cause the monitor to blank and change to a separate resolution. Some games still give the option, but the DWM still treats it like borderless fullscreen(no screen blanking between alt+tabbing back to desktop) when it composites the frames with MPO. Basically, there’s no advantage to using exclusive fullscreen anymore assuming you’re on a build of Windows from within the past few years.
Plus, straying away from a monitor’s native resolution introduces artifacts on the actual image displayed on the physical screen. They should always be ran at native resolution. You can use filtering options like bilinear/bicubic for down/upscaling an image and it will will result in a better image on the native resolution screen vs manually changing the display resolution to a non-native resolution on the monitor. And by native resolution, I mean at the hardware level, how many pixels are physically built into the display.
And again, it’s 2025… People alt+tab a lot and tons of people use multi-monitor setups. Though I’m sure they will eventually get around to fixing the setres issue in some way, shape or form.