Note that Group Policy is not part of Home edition of Windows 10. So, this method doesn’t work on Windows 10 Home edition.

First Open Group Policy Editor, by typing Edit Group Policy in the Start or task bar search box and then pressing Enter key. Click Yes if and when you see the UAC prompt. Now In the Group Policy Editor, navigate to the following policy:

Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options.

Here On the right-side, look for the policy labelled Accounts. Guest account status and double-click on the same to open its properties.

Select Enabled option and then click Apply button to turn on the Guest account in Windows 10.