Hi,
To remove that pop-up, please try the following steps:
Press Ctrl + Shift + Esc to open Task Manager.
Click the 'Details' tab.
Scroll down and look for the PC App Store icon(represented by an orange shopping bag; the process name may differ).
Right-click on it and select 'Open File Location.'
Return to Task Manager, right-click the PC App Store process again, and select 'End Task.'
If you want to completely remove PC App Store:
Go back to the folder you opened earlier and delete all the files.
After that, restart your computer and check if the issue is resolved.