I dont have the type of income to contribute to it EVERY year, but even if you use an employer’s 401k you can roll it over into yours as soon as you leave or are eligible
solo 401ks remove all the guess work and limitations of your other employer’s random plans. you can invest in anything, not just random vanguard mutual funds, you can borrow against them instantly instead of however long the bureaucratic machinations take, you dont have to ask anybody - people that dont know the answers that they should know
and most importantly, the annual contributions are just the first step, it grows tax free and should vastly exceed your contributions. once it independently has a big enough net worth it can be an investor in private equity and hedge funds’ feeders and be ready for some large moonshot bets or losses.
but remember, if you equate retirement accounts with the least risk possible, generic advice gets generic results. its more important that it grows tax free.
not advice, just what I do.