To make a long story short, formal or informal

I know from here a couple of good alternatives for "to cut/make the long story short", I'm just curious if it is formal to use it or not.

Solution 1:

It is an idiomatic expression (cliche - thanks @Accumulation) and, though it is polite, it is not formal in the sense that it would be out of place in, for example, a business proposal.

But that is contextual, since it would be acceptable to use the expression in diplomatic speeches.

It is somewhat casual and somewhat familiar. It might be in place in a testimony, but it would not be appropriate in a legal document.

All about context.

"To cut a long story short" would be even more casual.