Here's your checklist, in order:

Re-enable Copilot: Extensions (Ctrl+Shift+X) → find GitHub Copilot → click Enable AI Features (the global one, not Workspace)
Sign in: You'll get a prompt in the editor. Click it, enter your GitHub credentials once. Done.
Confirm Git is still off: Ctrl+, → search git.enabled → make sure it's still false. Same for git.autorepositorydetect.
Reload: Ctrl+Shift+P → "Reload Window"
Start typing code. You should see ghost-text completions within a few seconds.
That's it. One sign-in, then you never think about GitHub again. Your editor is clean, your system is yours, and Copilot is just a suggestion engine in the background.