Depends on the state. IRAs are not ERISA-qualified plans, it may have some state-level protection. https://www.irafinancialgroup.com/learn-more/self-directed-i...

Its fairly easy enough to setup a Solo 401k. While it could be difficult to send contributions to it directly, you can contribute to an IRA and then rollover into the Solo 401k.

Solo 401Ks are also useful for enabling backdoor roth IRA contributions. For those with traditional 401Ks, one doesn't want to roll them over into a traditional IRA as that would remove one's ability to do backdoor roths.

Against specifically bankruptcy? Yes. As marcus0x62 already noted they are not covered by ERISA which is what deals with 401(k) plans.

However, they are covered under the Bankruptcy Abuse Prevention and Consumer Protection Act (BAPCPA) of 2005. This covers up to $1 million dollars. (I've seen something that suggests if the IRS is a rollover IRA rolled over from an ERISA-qualified plan there might be no limit, but haven't looked to see if that is right).

Note that this just covers bankruptcy, whereas ERISA also covers seizure by creditors, so the 401(k) is better in this regard since you would actually have to declare bankruptcy in the case of an IRA. States usually provide protection against creditors. See the link in marcus0x62's comment.

Also if you do something stupid like use your IRA as security for a loan the BAPCPA protections will not apply. I've also seen something that said if you borrow money from your IRA it can reduce your BAPCPA protection.