The idea is to go for whatever that is currently accepted as low risk. For example, if bonds are considered risky, maybe high interest saving accounts are the next best option. And you can adjust your retirement goals accordingly.
interest saving accounts produce negative real returns, you cannot put enough money into one to generate the passive income you need to retire.
The whole retire early idea is predicated on substantial investment returns and the ability to outpace inflation. Savings accounts won't cut it.