First of all, I'm not sure what 'version' of Outlook you are speaking of, but there is no 'Gear" icon (for settings) in Outlook.
However, I do know how to look at 'compose messages' under options, and there is NO 'pop out replies and forwards' so this is not a solution.
Also, Turning 'off' the reading pane does nothing but turn OFF the reading pane. it has no bearing on the pop out window when composing new emails. So thanks, but both of your solutions do not apply.
FYI, the version of Outlook i am using is this
Microsoft® Outlook® for Microsoft 365 MSO (Version 2304 Build 16.0.16327.20200) 64-bit