The IRS rules do not specify what one may invest in with a self-directed IRA or Solo 401(k) plan. Rather, only a few asset classes are prohibited investments. An IRA may not invest in life insurance or collectibles.
Collectibles under IRC Section 408(m)(2) include:
Pretty much everything else is allowable, from conventional stocks, bonds and mutual funds, to real estate, stock of privately held companies, cryptocurrencies, and a whole lot more.
With a self-directed IRA or solo 401(k) plan, you have the flexibility to be fully diversified and to invest in what you know.
