I'm going to a bank, a shop, a dentist - I've found a new one and I may well be about to describe it to you.
"A nice evening" - there have been ones before, there hopefully will be again, this was one of them.
Well, that would work for many uses of the, but it's definitely not a correct explanation here. If I have no idea where the bank is, I'll still describe myself as going to "the bank". I could tell you that "I'm going to the bank", go out and get in my car, and then look up where a convenient bank is. This has to be viewed as idiomatic, or as "the bank" being an abstract task-based location rather than a concrete physical location.
Here it only sounds OK if you make the adjective stronger ("this was the nicest evening", though you'd probably avoid "nice" in this case and go with "best", "most amazing"...), or drop the adjective altogether ("this was the evening").
So nuance is that you might have many nice evenings, with this being one of — but what if you do not, and all are actually terrible except for this one? I guess with proper pronounciation of "THE nice", it can still work (we already talked about nice evenings and not-nice ones, so it'd be "this was the nice one"), but it'd be pretty awkward.
However it can makes sense if the surrounding context supports the idea of only one nice evening.
Grammar rules are generally about the surrounding context which allow us to leave out superfluous or repeated information and still be understood. Things sound strange when that missing information can’t be deduced from context.
"I have the son" sounds odd, even if there is only 1 son on your mind.
Edit: Here's a frustrating HN thread where someone tried to claim it makes sense, but it turned out his argument hinged on "well obviously all native English speakers regularly go to some store, right?" Screw the homebound.
I think the usage falls into this group: "The first group consists of nouns which refer to shared knowledge of the situation or context...",
When you're talking to people you live with it is true that they know which store you are going to. Friends and neighbours would have also have known up to fairly recently, when people still mostly walked for groceries and such to the few small stores nearby and made friends with people who lived close.
So, I'd say it's a bit of a colloquial hold over from walking times and construction taking a listener into confidence.
But again, people use this even when I have no reason to know which store they went to.
I’m not necessarily saying they should stop doing this, but it’s clearly not the usual kind of definiteness implied but the use of “the”.
A prescriptivist pedant might insist that this is incorrect, and they should instead say "I need to go to a store", but in my judgment as a native speaker, the version with "the" is more idiomatic, and the version with "a" sounds stilted.
To repeat another part of my initial post, it's like the use of "the" in "the bigger they are, the harder they fall". It's clearly a different usage/meaning/sense of "the" -- in fact, most other languages use a different word for that sense. (German uses je ... desto.) It would be very dubious to explain all uses of "the" as "oh its when the noun has definiteness". It wouldn't cover that case, and it wouldn't cover (the typical use of) "I went to the store".
Some of the statements (by other people) in this conversation are wrong, based on applying a school-style oversimplified explanation that doesn't really match English usage.
How can this be in your example? When I am saying "I went to the store", I am really saying "There are a group of locations that I could have gone. E.G., the car dealership, the bank, the museum, the store, or the office. I went to the store".