You can take a screenshot in Editor using the Python console.

1. Open the Python console in the Editor and run

import azlmbr.bus
import azlmbr.atom

2. In the Editor viewport menu set the resolution to Custom and enter the width and height you want (e.g. 4k or higher)
3. In the Python console run

azlmbr.atom.FrameCaptureRequestBus(azlmbr.bus.Broadcast, "CaptureScreenshot", "Capture1.png")

This will write a PNG file named Capture1.png to your project's Cache folder.