Install uBlock Origin and add this rule to your filters, blocking this cruft even when Copilot has been technically fully-disabled site-wide in your GitHub account options:
github.com##button[data-testid='open-in-copilot-agent-button']:upward(div[data-testid='sidebar-development-section']) /* swy: 'Code with agent mode' button in every issue */
github.com##a[href='/settings/copilot'] svg.octicon-copilot:upward(li[class*='prc-ActionList-ActionListItem']) /* swy: 'Your Copilot' option on sidebar */