The annoying Microsoft Store app icon is appearing even if you unpin it from the taskbar. After reboot, it will reappear again.
To permanently remove this icon, you need to unpin it from the taskbar and then disable its policy.
- Right-click on the icon and select unpin from taskbar.
- Run gpedit.msc to open the Local Group Policy Editor.
- Navigate to User Configuration > Administrative Templates > Start Menu and Taskbar > Do Not Allow Pinning Store App to the Taskbar.(It is easier to find the policy by sorting it by setting name)
- Disable the policy.