Should FPS be impacted this severely?

‘Disconnecting’ Editor Windows halves FPS ?
I mean simply detaching & pinning to 2nd monitor.

Can this be corrected ?

if youre using NVIDA control panel to cap your framerate, this is the issue. You must run unreal editor uncapped

There’s no limit in-place. I get 120 FPS frequently enough.

Though the scenario I was describing went from 60 : 30 - back & forth.
Depending upon whether or not I moved my Outliner Window over to my secondary-display.