No such thing as FU money. As you get more you want more, or if you don't then your spouse does. There is such a thing as "I can tolerate a 3-6 month job search no problem and not jump at the first opportunity" money. It makes 90% of the difference, especially in the long run.
Of course there is such a thing.
Lifestyle inflation is a known phenomenon which you (and your spouse) can choose to avoid if you prioritize it, not some immutable rule of nature.
If the treadmill of accumulation that lets someone believe "there's no such thing as enough" ever stops, I think they would be shocked at how quickly they realize what enough actually means.