I have implemented community site for Salesforce mobile App and Desktop both. But when I login my Salesforce sandbox in mobile or Desktop, In the App Launcher section Community site is not Visible in sandbox. Similarly, I have done this in my personal developer org, where the site is visible in App Launcher section. Is there any permission that is required in Salesforce Sandbox so The community site visible in App launcher section?
You have to set that particular site to visible in app launcher as below.
Go to setup-> User Interface-> App Menu-> and make sure the site is set to Visible in App Launcher as shown below
Please find the below Knowledge article for more details.