English proverb for when a solution comes too late

In Flemish we have a saying "Vijgen na pasen". Translated: "figs after Easter".
It means a solution comes too late to be of any use.

What is the English equivalent for this?

Some googling gives me "Closing the barn door when the cow has bolted", but the explanation seems to point more towards the wrong solution for a problem.

The standard idiom has to do with horses rather than cows:

closing/shutting the stable door after the horse has bolted
trying to stop something bad happening when it has already happened and the situation cannot be changed: Improving security after a major theft would seem to be a bit like closing the stable door after the horse has bolted.

While the above is not an exact match, it can be adapted to serve your needs. You could simply say that the horse has already bolted, which would implicitly connote lateness.

Other common phrases that revolve around lateness include:

• Too little, too late
• A day late and a dollar short

You were close with the cow and the barn door. It should be

It's too late to shut the stable door after the horse has bolted.

Another is

It's easy to be wise after the event.

"A day late and a dollar short" is an expression used in situations you describe. Essentially, the solution is available but is of no use because of the delay in formulating it/

Taking a saying from a language you do not speak and trying to "translate" it is hard enough, given the challenging nature of idiomatic words and expressions. Coming up with an equivalent saying in a language you do speak often compounds the difficulty.

Frankly, other contributors to this post have beaten me to the punch with "20/20 hindsight," "Too little, too late," and "A day late and a dollar short."

While this may not be an answer to your question, it is somewhat apropos nevertheless. The French, I am told, have a saying that could be translated into English, roughly, as "brilliance on the staircase"; that is, thinking of the right thing to say when it's too late to do any good. Say some smart aleck at a party (or wherever) aims a snide comment at you. You are temporarily rendered speechless or you blurt out something feckless like "Oh yeah?!" Then on the steps as you leave the party you think of the perfect riposte, but it's too late. (D'oh! as you smack your forehead). Is there an English equivalent?

Well, how about "That ship has sailed"? Or, "Monday morning quarterback?" Or, "We get too soon old, and too late smart"? Or, "Why didn't I think of that!?"? Or, "You can't reinvent the wheel"? Or, "You can't un-fire a gun"? Or, "You can't un-ring a bell"? Or, "That's water over the dam"? Or, "Beating a dead horse"? Each one of the foregoing has a flaw or two, I suppose. Any other suggestions out there?