Earlier quoted context omitted.
IRAs have income limits. Series I bonds by definition only keep you level with inflation. Which doesn’t help if house prices, rent and healthcare continue to outpace inflation. L
As you probably know, if you are above the normal IRA income limit, you can sidestep the limit for at least a Roth IRA via the Backdoor Roth [1] by converting post-tax IRA contributions to a tax-advantaged Roth. There are a few rules you need to keep in mind, but it's a good option. You can also use an in-service distribution to move after-tax 401(k) contributions into your Roth IRA, the so-called Mega Backdoor Roth…
Most companies don’t let you do that directly. Mine allows “after tax contributions” up to 10% of base. Not to be confused with a Roth 401K.