No experience, I'm afraid, but bumping this for others who might.
I don't think most employers will see this as an issue - small businesses fail all the time!
A lot would depend on what the business was, how long your break in paid employment was etc.
I think your CV would highlight your 20+ years of experience so you wouldn't need to highlight it as such, nor explain too much why your business failed. As with all job applications, you need to tailor your application to the role they are trying to fill, so matching your skills to what they are looking for. If you write a good application you'd get an interview.
At interview you might need to expand a bit more on it - if, for instance, you left a career to start a business in something completely unrelated and were now trying to go back to that old career, did it mean you were disillusioned with the industry before? If so, what has changed to make you now an enthusiastic employee? That's the sort of thing you might need to think through.
But in my sort of work people have side gigs and paid jobs and often move between freelance and contract and permanent etc and it is not an issue.
As I say, a lot depends on the exact situation. I think you'd find it harder to explain a MLM type of business or franchise than some others?