I don’t think that dollar amount is entirely accurate. In my region, 70 grand is barely a working class income. Middle class doesn’t really kick off until 100-150k. Then again, if I can get out of debt and build my RV/tiny house, I could be pretty happy on >$20k a year.
But yeah, I’d say you need enough that you no longer worry about basic needs (now and future), and have enough left over to do whatever thing makes you feel good about life- Any more than that doesn’t really make that much difference.