Object Properties grayed out on elements in Content panel, unable to edit tags or content

@leighmurP this might be a the limitation by running Acrobat Pro 2020 on a newer operating system like macOS Sonoma 14.7.1. Older versions of software can sometimes have these weird quirks or limited compatibility when interacting with the deep-level PDF code, making a simple function like editing an object's properties unnecessarily difficult or restricted. 

It seems the problem of those grayed-out fields is likely due to two things working together: how the PDF file was built and which Acrobat version you're using. When you look at those small bits of musical notation in the Content panel, you're seeing the PDF's basic "building blocks." The program that created the sheet music probably didn't save those little marks as regular text or figures. Instead, they were saved as "low-level paths" or "containers"—think of them as simple digital drawings that are too basic in the PDF code. Because they're so basic, Acrobat can't easily give them a proper tag or alternate text. The grayed-out fields are Acrobat's way of saying, "I see this object, but it's not set up in a way that lets me add an accessibility tag here."

The good news is that your solution—labeling them as artifacts—is the perfect fix! Musical notation is usually just context or decoration to a screen reader, so marking it as an artifact is the right and best way to pass the accessibility check.