I can’t download my iOS 15.5 to iOS 16 , the download and install menu is not appearing

Do you have a MDM profile? If so -> Contact your company - IT department.

Hace you install / use iOS Beta version, then remove the beta profile (Settings -> General -> VPN & Device Management).

Then Restart your iPhone and check for updates again.

It might depend also on your iPhone model.

See this compatibility chart about that, and check if your unidentified iPhone model supports iOS 16: