What you want IINA to do:

• Conveniently show the currently playing media's file in the Finder via menu command.

• Even more conveniently do so with a keyboard shortcut.

Of the two, I think the keyboard shortcut is more important, so I'd be happy with that without the menu item. I vote for a default keyboard shortcut of ⌘R.

What IINA does currently:

The only way that I can find to do this is by showing the playlist, right-click the item, and choose Show in Finder. It is a pain, and it is not keyboard-shortcut-able.

One can right-click on the filename in the titlebar, then click on the containing folder in the dropdown that appears, but this is also inconvenient and not keyboard-shortcut-able.

Why you think this should be added:

It's a common need.

IINA has a File:Delete Current File command, so it seems odd that the more general ability to do whatever you want with the file via the Finder is missing.

Examples of other projects that have something similar:

Many apps have such a menu command, though named differently:

Show in Finder: XCode, macOS Dock, BBEdit
Reveal in Finder: Sublime, Transmission, VLC
Open in Finder: Jetbrains IDEs
Open File Location: Typora