See title. In 1.15.2 and below, they used to show the subtitle, even if the sound was muted, or the event empty, as long as the player was in hearing range of the sound source location, it used to show the subtitle. Doesn't affect the master slider; if that one is off, subtitles still show.
Steps to reproduce:
Turn on subtitles
Turn off Weather volume
/summon lightning_bolt
No subtitles show in 1.16, but did in 1.15
Linked issues
is duplicated by 4
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Comments 4

In case of lightning, though, it's always so loud (especially with sound resource packs that change the file), because of the volume it plays at, the slider is almost unresponsive, hence why I turn it off, doesn't mean I don't want to know about it. Additionally, for the empty events, that was incredebly useful for debugging without having the actual sounds yet.
Regardless, it's different from 1.15, not mentioned in any changelog, and doesn't seem to have any upsides to have it this way.

If the slider isn't very good, make an issue on the slider, not the fact the game isn't telling you about sounds that aren't playing.
Well done on missing the whole point of the report...
This seems like it would be intentional? If you've turned off the slider for a specific sound type, that means almost by definition that you don't care about those sounds, so not showing subtitles for them seems sensible.