Investing for minors: 529 accts canNOT hold individual stocks directly; what about ETFs?

The 529 plans with which I'm familiar only allow investments in Mutual Funds -- and only certain 529-tailored funds at that.

At the other end of the spectrum, there seems to be a universal prohibition against buying individual stocks in those accounts.

In between are Exchange-Traded Funds. It's not clear if I can buy any old ETF that I like inside a 529 acct, or only a curated subset of them.

Need advice from those who've trodden this path before me.

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OK, half an hour in, so far so good. Best one-line summary: *"You can ONLY buy what’s available in your 529 account".*

1) This implies that a Fund House offering 529 accounts will probably offer ONLY their own funds in it.
2) Does anyone have any experience with a 529 plan which DOES offer ETFs, not just Mutual Funds?