Find my iPhone icon has disappeared

Hidden is not quite the same as disappeared.

Go the Home Screen

Keep swiping Left until you see the App Library

Is Find My there? If yes, hold on the icon until it wiggles and move it back to where you want it

If not, type Find My in the search box and tap Go

JJmestephenson wrote:

The icon for 'Find my iPhone' used to be on my Home Screen

Be very careful. The “Find My iPhone” is obsolete. It was replaced by Find My (no iPhone) with the introduction of iOS 13 nearly five years ago.