The easiest method is starting troubleshooting with simply disabling Game Bar. This could be helpful to remove the key combination and use it for other purposes. Now, you can take these steps:
Press the Win + I combination key to open Windows Settings
Go to Gaming > Gaming bar.
Switch the toggle of Xbox Game Bar for things like recording game clips, screenshots, and broadcast using Game bar to Off. Next, press Win + G to see if the error is solved.
More details you can find here https://www.minitool.com/news/ms-gaming-overlay-popup.html
This message is displayed if you try running multiple Quantowers in parallel on the same computer or you have closed Quantower a few seconds ago and it did not finish closing yet. In 20 seconds or sooner Quantower can be started again.
If even after a few minutes the platform fails to start, go to the Task Manager. Press Ctrl+Shift+Esc to open the Task Manager with a keyboard shortcut or right-click the Windows taskbar and select “Task Manager.” Find the process with the name "Starter", select it and click on End task.