Best practices
If search is important, consider making it a primary action.
Aim to make your app’s content searchable through a single location.
Use placeholder text to indicate what content is searchable.
Clearly display the current scope of a search.
Provide suggestions to make searching easier.
Take privacy into consideration before displaying search history.
Systemwide search
Make your app’s content searchable in Spotlight.
Define metadata for custom file types you handle.
Use Spotlight to offer advanced file-search capabilities within the context of your app.
Prefer using the system-provided open and save views.
Implement a Quick Look generator if your app produces custom file types.
For the complete guidance, including worked examples and illustrations, see the canonical page: https://developer.apple.com/design/human-interface-guidelines/searching