I've changed careers a few times and am now in salary maximizing mode (maybe should have done it before, but I was in "save the world" mode).
I've wrestled with this question a lot. For my family, I'm willing to love in our medium cost of living city in a sit urban house with 4-6 weeks of travel a year once we have an empty nest. In that case, I think that $5m is enough. At 4% that's $200k a year, which feels good.
However, I'd really like to land at $10m. Eliminates some of the tail risk and creates more freedom for better trips, and maybe even a chance to spend the extreme seasons in a different location.
If you want to do 6 months of travel and live in expensive places, $15m might not be enough.
And, if you live wisely and have a strong family and network, $1m + social security might be enough. Some people would love to live in the same house as their adult kids, and that would mean you'd need a lot less.
Edit: also staying healthy to address medical bills concerns. Health care industry seems to be on track to take all the money you have, so doing what you can to avoid preventable diseases definitely changes what your optimal number should be.