What is ATM10? Minecraft 1.21+ / 500 Mods Loaded / Shaders / Quests / Fun endgame goal. Plenty of content to enjoy in a casual way! No worries : it's simple to join!
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Now, you may be thinking, "The hell is an ATM10 & what's a java minecraft?" well, I'm sick and am piecing this together on the fly so you're getting the barebones. Anyway, there's a few tools that'll make your life easier; if you're a WoW player, you should already have curseforge. Curseforge is an allrounder modpack launcher & downloader, iirc it even downloads the needed java version for whatever pack you're playing. I personally don't use it, so my advice would be useless. I use something called Prism which you can obtain here (It's the Prism launcher) I'd personally advise allocating 8192mb, you can always crank this up later

Download according to your operating system (Likely not arm64) and launch it. From there, login. After that, press 'Add Instance' and navigate to the Curseforge section. You'll either see ATM10 instantly, or, you'll have to use the search bar to grab it. After that it's business as usual, press launch & it should be smooth sailing.
ATM10 is a mostly kitchen sink pack, there are a handful of gated things in progression but it's just enough to keep vet modded players & new modded players interested. Tamable dragons, bosses, technology & big moving factories are things to do. There's some screenshots to help whomever along