Dr Jekell

You have a few choices:

• Minecraft launcher (official) - Allows you to play vanilla MC.

• Prisim launcher - allows you to download & play mod packs from several sources (newer FTB packs have to be loaded up in the FTB app first before being imported).

• FTB app - allows you to play basically any FTB modpack.

The first should show up in the software store and the second two have install instructions on their websites.

You have to load it up in the FTB app then import it into Prism.

Twitch already has a dark mode available in the settings.