You are, of course, technically correct but I can’t say I’ve ever heard it used outside of old books and plays, or fiction set in the past.

My dictionary says it's "archaic".

How? What is a common modern day use?

Obviously Americans know it from the Gettysburg Address where Lincoln referred to the US being founded "four score and seven years ago", but he was being intentionally poetic, but you may not count 19th century as "modern" (even though from the linguistic perspective it is), but people often say things like "there are scores of movies where the protagonist finds out he is a prophesized hero" even today.

That usage (“there are scores of x”) is figurative and doesn’t literally mean “20 * n”.

The same meaning of a group of twenty. "There must have been a score of cars at the drive-thru." It hasn't changed.

It's barely ever used nowadays though, whilst 30 years ago you'd hear it occasionally, similar to a gross, or things being referred to in yards. It's changed IMO.

I think it's part of how we've tended to remove dialect and en-gb terms as we've more intra-UK mixing and more non-UK born residents?

You might not hear it often, but that doesn't mean it's barely used. English is spoken by more than just English people. I reckon I hear "score" used in the sense of twenty of something than I hear words you'd probably describe as more common, such as "laden" or "bereft."

Might I enquire the context and locality where you hear 'score' used?

You are right, I mistakenly assumed we were talking about en-gb.

I live in the southeastern United States. It's common for conveying the size of a group, for instance. If a lot of people showed up to an event but not on the scale of hundreds, it's common to hear "scores of people."

It's not common in my job to talk about scores as a metric because 20 isn't a natural unit for my work product, but I wouldn't be surprised to hear it like that, either. We still use "dozen" and "gross" for other non-decimal groupings much more commonly, e.g. "a dozen doughnuts."

As someone who has lived in the west and northeast, I’ve never heard the word score used to mean 20 outside of Lincoln’s address. In most dialects in the US, scores has just been relegated to another synonym for many and doesn’t get used outside of it’s plural form. Interesting to hear that there are places that still use it occasionally, much like I occasionally hear “gross” used as you mention.

I think it's still used a bit in British English, along with other things that strike the American ear as archaic like 'stones' and 'fortnights'.