having visited my grandparents and discussed their finances with my Dad a few weeks ago (part of a conversation about retirement communities, long-term care, insurance, wills, etc for both sides of the family) I'm less convinced that the $1m invested number that I've generally used as a ballpark is as necessary for most people. My grandparents have ~$450k, but own 2 houses - one in AZ for winter, one in upstate NY for summer, are both getting SS, and sold a strip mall, financing the purchase for the buyer, so they get some income stream. They live on about $20-25k a year, and are pretty happy with their lifestyle. Now, they get SS and medicare, and don't do much, but in some ways it's a comfort that I'm not worried about them falling off a financial cliff.
For myself, I still think that $1m is a pretty good ballpark for FIRE, but seeing people happy on less is some comfort.