I remember that normally while changing volume or aspect ratio from shortkey or mouse wheel, I was seeing a volume info or the aspect ratio in numbers displayed on the video for several seconds.
But now this is disabled. How to enable it?
This is called OSD: 'on screen display'.
The setting is under Tools > Preferences > Show settings: All > Subtitles/OSD: check On screen display
:-)
Sometimes, even with OSD enabled, nothing gets displayed, but I stumbled on a "solution" for this. Enabling/selecting a visualization brings back the OSD text.
Audio -> Visualizations -> Spectrometer
(You can try any of the other visualization options you prefer, but don't leave it on "Disable").
Unfortunately this is a bug that happens with VLC now and then.
Sometimes when you are watching a series of videos, the OSD will show as expected on the first video, but when it switches to another video in the playlist, suddenly the OSD will cease to function. Stopping the video (not just pausing) then playing again will fix it. It is not convenient, but it works for now until the devs can fix the bug.
It's the OSD, sometimes the text disappear because you change the subtitle font. On Mac some font will not show, specifically ones that are not English. You will have to choose between displaying your subtitle in foreign languages or displaying the OSD text.