the regular java version runs natively and runs really well, you can also try some of the older versions that people have pre compiled to run stand alone. there are also a few reimplementations like classicube but that's really limited. I've genuinely never pirated Minecraft actually so I'm not sure how you go about it.
You can use an offline account with Prism Launcher (I recommend flatpak), but only if you've logged in with a Mojang or Microsoft account at least once, or found some other way to bypass that requirement. It has integrated mod support and you can have completely separate game instances.