Holding Tab key used to underline letters for keyboard shortcuts - not anymore?

Holding Tab used to trigger underlined letters across the Task Detail pane (possibly also elsewhere, I don’t remember) indicating which letters to use as part of the keyboard shortcut.

This no longer seems to be the case - is there a reason for this? Is it intentional, or did I break it somehow?

I’m using Chrome Version 74.0.3729.131 (Official Build) (64-bit).