1) Open the Desktop.com app
2) If you already have apps added to your desktop, click + Add button inside the Apps section
3) Alternatively, if you do not have apps section, click blue +Add button and then choose Add an app option in the drop-down menu
4) Click Create Custom app button
5) Now, if you have a free Google Account you need to make your custom app URL looks like: https://firstname.lastname@example.org . Where [email@example.com] should be replaced with your actual email address.
If you have a paid branded Google Workspace, your custom app URL will look like: https://firstname.lastname@example.org. Where [email@example.com] should be replaced with your actual email address
Click Add application button once you've entered information
6) Now your Google Mail account has been created as the custom app and you can add this to your desktop