i could be wrong, but aren’t libraries intended to be separators for different types of media? in the jellyfin docs on libraries it directly states mixed media libraries are discouraged due to incorrect metadata. collections do sound like a good idea, but it lacks the visual and information aspect about the series i’m looking for. still, it does sound like the best choice so far
the specific artbook of the picture you posted is available on archive.org with the title “evangelion material”, you can download it separately with the torrent they provide. the internet archive actually has a pretty impressive artbook collection, though i actually found that specific file under a mirrored torrent on one of the dht search engines on the megathread, which are surprisingly helpful/extensive, though a lot of torrents (especially older ones) aren’t being seeded, but it’s a good start once you have the filename.
as for non-english forums, i’ve had luck with baidu search: you’ll be mostly looking for pan.baidu links in animanga forums/sites (which may be hidden behing login walls, but most of the time you can use google’s cache view), though you do need an account to download from them, which can be difficult to get depending on your location. one specific forum that seems to have a lot of content not available elsewhere is otomedream, but it’s 1) very difficult to get in, i’ve been on the waitlist to get my account approved for like two months; and 2) requires you to use their currency to get dl links to the actual content. also worth checking out is vk and japanese+chinese torrent aggregators and book download sites, fmhy has some in their non-english section. in most of these, you’ll have the most luck searching the original japanese title in quotation marks.
i can’t personally attest for private trackers like bbt and ab, but i imagine it’s worth checking out if you have an account.
did you ever figure this out? i’m kinda in a similar situation, though i ended up just using a downloader for the clip studio online reader they provide
oh yeah, i love qxr/tigole releases, they’re def my go-to when it comes to extras, just figured i’d ask in case anyone knew any other sources (+ any movies that they don’t have the extras for, like everything everywhere all at once). also yeah, i knew that, just don’t know what to download in iso rips specifically, since from what i’ve seen the extras aren’t named differently from the main movie itself