"Dollars used to be backed by gold and it was still fiat money." - This is just plain wrong.

Fiat money means exactly a government-issued currency not backed by a commodity such as gold.

https://www.investopedia.com/terms/f/fiatmoney.asp

I'm questioning Investopedia here.

Fiat is typically contrasted with commodity or representational currencies. The key element is that fiat has no intrinsic value. It's usually issued by a government, but need not be. The value comes from faith.

Bitcoin meets all the qualifications save government issuance. The bits themselves have no value. The currency's value is based on faith in both the underlying computations and in the existence of a market for trading bitcoin.

Wikipedia gives the definition "often by government regulation" (implying not necessarily) citing Goldberg, Dror (2005). "Famous Myths of "Fiat Money"". Journal of Money, Credit and Banking. 37 (5): 957–967. doi:10.1353/mcb.2005.0052. JSTOR 3839155. S2CID 54713138.

That definition is wrong. "by fiat" does not imply a commodity, it was just one of the many alternatives

By which definition Bitcoin is still not a "fiat" currency, since it is not government-issued.