Where the settings are

Settings is at the bottom of the sidebar (or Ctrl+,). Its sections: General (theme, backgrounds, language), Models, Cloud models, Pictures, Web search, Tools (switch tools on, the tool catalogue, panels, the "/" tool list, the calendar, media and timers), Voice, Files (search by meaning), GPU, Storage and Desktop (desktop app), Chat history, Security (block all network traffic, offline chats, incognito chats) and About (licences). The sun or moon button at the top switches light and dark.

This guide is the same text GlirOS itself uses to answer questions about GlirOS.