The Text Background Opacity and Action Bar Background Opacity found in the accessibility setting does nothing no matter the %.

The Action Bar Background Opacity should make the black bar behind the item's names disappear or lessen in strength (depending on what setting you put it on) and make it look just as how Java looks when an item's name pops up, but the setting is broken and changes nothing.

The Text Background Opacity should make the black bar disappear or lessen in strength (depending on what setting you put it on) when any sorta text message appears on screen as well as the black bar behind the coordinates.

How to recreate this:

Go into settings then accessibility settings and change Text Background Opacity and Action Bar Background Opacity to zero. Then get an item and equip it so its name pops up for a temporary amount of time and check to see if the black box is behind the name. if it's still there Action Bar Background Opacity isn't working. To check the Text Background Opacity just type in chat, or make a command block say something on screen. If that doesn't work then Text Background Opacity isn't working.