In my opinion, the best way you can support local arts and culture in Japan is to buy far more doujinshi than you'll ever reasonably make time to read, and to then never stop adding to the pile.
for people overseas, you can get digital editions of doujinshi on DLsite, and the majority of them are DRM-free (not all of them, it's up to individual artists, but the product pages will clearly indicate if something's DRMed). There's also a decent chunk of stuff that's been translated into English, they've got a program that offers scanlators a way to go legit and share profits with artists.
DLsite's been dealing with a bunch of bullshit from US credit card companies lately, but so far they've been decent about actually having a spine; as far as I'm aware, they haven't added any restrictions on what sorts of stuff artists can sell, just some limitations on what you can write in product descriptions (words like "hypnosis" have to be censored, that sort of thing). Right now, the easiest way to buy stuff from them if you're in the US is to buy a point code on https://dl-pay.com/ (this is an official site they run, it's also linked in the "points" section of your account page), redeem it, and then buy doujins with your point balance, 1 point = 1 yen.
i ended up writing an increasingly-elaborate CLI tool to organize my digital doujin library into a nice collection of local HTML files I can open in Firefox to browse through the collection. it's very much a "works for me" piece of software, but if anyone wants to mess with it: https://git.xeno.science/xenofem/dlibrary