Currently people are pessimistic about stock market returns going forward so it could be lower (3-3.5%). And even lower if you want it to last longer than 30 years.
The market historically has been going up, so at least historically it's been reliable to get a fixed income. I don't think $2M is sufficient to retire very early, mostly because of bad years and that your initial capital loses value over the years, but it can generate a nice income and most people can have something on the side that generates some extra money as needed. With $4M I would be more comfortable retiring at 40 let's say, depending on cost of living of course.
"Fixed Income" is more about structurally reliable and consistent returns, rather than historical average returns.
An outlier bad year can easily wipe a huge percentage of capital invested in stock--but the younger you are, and the more buffer you have, the less likely this is to be a problem. But don't mistake that for fixed income!
Fixed income usually refers to interest rate products, and as mentioned above in this thread, the inflation-adjusted rates have been pretty bad. Pretty much since the start of Quantitative Easing, I believe.
You could buy an annuity from an insurance company. A quick Google search shows that $2mil should buy a 40 year old about $70k/year for the rest of their life.
