Apple - Keyboard shortcut to focus application's search bar (not Spotlight) in macOS?

I don't believe there is a system-wide shortcut for this, as the definition of Search Bar may not be standard across apps. But hitting ⌘+F focuses the Search Bar in many Mac applications.

As already noted, most applications use Cmd+F for search. However, in some applications Alt +Cmd+F triggers the main search dialog (e.g., iTunes) or a secondary form of search (e.g., Excel, Finder, Safari, Chrome).