DualGrade is installed at /Applications/DualGrade.app.
If you selected Accessibility refresh, enable DualGrade in System Settings → Privacy & Security → Accessibility. Use + to add the installed copy if needed. Then reopen DualGrade.
If approval is already working, you can deselect that component on future installations. The installer does not reset Input Monitoring or delete your profiles.
Connect your controller, select a profile, and click Enable. Choose an L3/R3 control to assign left or right mouse click.