Stress and burnout is real. When you have FU money, semi-ER becomes a tempting option.
^ This. In retrospect, knowing we'd end up choosing to do sporadic part-time work (and that said work would add up to a decent income), I wish we'd gone FIRE sooner. We were just scaredy cats and waited until we paid off our SF Bay Area mortgage (not representative of today's astronomical home prices, as we bought a VERY small house near the bottom of the Great Recesssion/late 2012).
We're 5.5 years into FIRE now. After our initial six months of lay-about, sleep lots, burnout recovery, we ended up taking on very casual, ad hoc, part-time work. Depending on the year, we've had $55k-$97k in income, usually more in the $65k-$75k range before expenses and deductions. We haven't touched our savings. 5 stars, strongly recommend, would do this lifestyle again.
To answer the original question, that would have been about $800k without a paid-off house, to be FI and keep working. Instead it was $1.5m + paid-off house that (in today's ridiculous Covid bubble market for single-family homes and comps on our block, has an estimated value of $1.4-$1.7m, 3x what we paid ~8 years ago). When we were able to FEEL FIRE in our bodies -- how much better we felt, better sleep, everything -- I wished we'd done it sooner.