I was wondering whether someone here might help me remember a movie title.
It was a sci-fi horror film from the early 2000's wherein a darkness was gradually enveloping the world. By darkness, I mean just a complete lack of light, a black void. I don't think the origin of the darkness was ever shown to have been determined, and it's possible that the advance of this darkeness is triggered by movements or sounds, but that's a guess.
I very vaguely remember one group of people were trying to survive inside a public place, like a store, while there was another group staying in a bar.
It was definitely a B-quality film, in English and possibly only released on VHS. No big-name stars that I remember. It was not a film I had heard of before or since. I've scoured IMDb with no joy.
Ring a bell with anyone?

I didn't know which exact movie are you talking about, so I asked AI bot to answer to you description and here are the titles it suggested:

1) The Dark Hour / La hora fría (2006)

The Plot: A low-budget Spanish sci-fi horror film set in a post-apocalyptic facility where survivors hide from an entity/cold darkness that sweeps through the corridors. Released straight-to-video around that timeframe with no big-name American stars.

2) The Mist (2007)

The Plot: A strange mist/fog envelopes a town while people are trapped inside a supermarket. (Though it's fog rather than complete darkness, the "trapped in a store" premise fits very closely).

3) Darkness (2002)

The Plot: Forty years after a dark ritual vanished a group of children, an American family moves into a house in Spain where an ancient force—a pitch-black, enveloping darkness—is trying to complete the ritual and swallow the world during a lunar eclipse.

The Details: It fits the early 2000s timeframe perfectly and definitely has a dark, pitch-black void vibe, though it focuses more on a family/house setting than public places or bars. It was a lower-budget production with direct-to-video/VHS releases in many regions.

For me the movie from 2002 suits the best to the described detail.

4) Vanishing on 7th Street (2010)

The Plot: An unexplained, almost sentient darkness gradually envelopes the entire world, making people disappear into thin air and leaving only their clothes behind.

The Location: The surviving characters gather inside a bar running on a backup generator to stay in the light, while others get trapped in public places early on.

Note: It came out slightly later than the early 2000s and has a couple of known actors (Hayden Christensen, John Leguizamo), but it heavily feels like a low-budget B-movie.

5) Phantoms (1998)

The Plot: An ancient entity/black void wipes out an entire town. A small group of survivors moves through deserted public places, shops, and bars trying to figure out what is happening while staying alive.

Note: Fits the late '90s/early 2000s VHS era and B-movie atmosphere.

That's the one - thank you for your help.
I have to learn to use the Internet. I was using search words like night, dark, void etc. I never used the word vanish.
Also, btw, anyone reading this and thinking about finding it somewhere and watching it, don't waste your time, it sucks. It has a well-deserved rating of 4.9 on IMDb, where anything below 6.5 is iffy. I had no particular reason for wanting to find it, other than to satisfy some unexplained hair up my ass.
Here's the IMDb listing, which includes a trailer.
Hey, it's actually on Tubi right now.

Vanishing on 7th Street (2010): The population of Detroit has almost completely disappeared, but a few remain. As daylight disappears they realize that the Dark is coming for them.
My Comment: Having watched this again now, after about 15 years, it turns out that the creeping darkness are shadows of dead people who kind of come together into a big blob. The only way to keep it/them away is to stay within a source of light at night. It's a somewhat intriguing concept, but the film just doesn't lead anywhere. A small group of people huddle for a night in a bar that has a failing electrical generator in the basement that barely keeps the lights on. The main protagonist decides that they need to escape out of the city, although it is never explained how that would solve their dilemma. Some die, some survive, standard Hollywood boilerplate. Not worth the hour-and-a-half.
Bad (1-4)
Watched on Tubi.