However, even if I release my finger thinking I've made a long press, there are cases where it isn't recognized as a long press and is still recognized as a tap.
Of course, it's fine if I hold down the key long enough, but since it's a shortcut I'll use hundreds of times, I don't like to keep long pressing it for any longer than necessary.
So I thought it would be good if there was a pop sound when it recognized that a long press had been made, so I'd know when to release my finger.
I doubt it. It might be a feature that could be added to KM, but I doubt that too. But I see your point.
There is probably a way to change the duration of the long press. KM has some internal variables that might be able to address this. It sounds like you need a shorter duration. Hopefully someone can tell us both if that's a setting that we can change.
There is a macOS command that can list dozens of KM's internal variables. Here's the command. Enter this command into a Terminal window. Perhaps one of them looks like the variable for the double click time.
That command will only reveal defaults that have been set; it won't reveal defaults that can be set but are not currently set, i.e. hidden preferences. To find those, you have to use strings command on the binary itself, though I don't even know if that works any more.
