When pressing the Open Marketplace button in UE5 or the Marketplace button in UE4, nothing happens. This occurs in both UE5 Early Access and UE4 4.26.2.
Tested in //UE4/Release-4.25 @ CL 14469661 and this did not occur, so marking as a Regression.
The Unreal Engine Marketplace does not open in the launcher
The Epic Games Launcher comes into focus and opens the Marketplace tab
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-117624 in the post.