As an indie author 1 and 2 are spot on. Amazon offers us the best royalties and the lowest print costs. Plus Kindle Unlimited is nice to be in too. I am not Amazon exclusive with all my books, and a common other place you can find indie titles is B&N! Also indie bookshops, authors’ kofi and patreon shops, itch.io and bookshop.org. But Amazon is one of the easiest places you can support indies as unfortunate as they are as an overall company.
Ofc you can always look for their books elsewhere (their website is probably your best bet to see where you can find their books) and you can always reach out to an indie author to see if they have other options besides Amazon, but sometimes unfortunately that’s your only option if there are specific authors you want to support