Like you, at one point I was looking for the best interior design business books. And sadly, a lot of them are out of date or boring.
Some of them are really old and I feel like the design business is really taking a transition that isn’t widely documented yet in the book world. You can always learn from other in business and what they have done.
So I did what I had to do, I learned from others (even if they were in another field). Business is business.
If you’re ever looking for something to read, check out some of the books I have read and really enjoyed.