As mentioned in bug 1841021, the CSS Properties and Values API gives custom properties semantic meaning by attaching additional information to them.
This information should be displayed within the Rules panel.

One way to do so is to extend the current tooltip showing the current value of the property by those pieces of information.
There might also be a link to the @property rule in the Style Editor when registered via CSS or to the registerProperty function call in the Debugger when registered via JS.

Sebastian

Looks like Chrome DevTools are implementing something that looks like this: https://front-end.social/@bramus/110932815004882288