What I actually did was:
- Exit 1Password (from the macOS menu bar, click on the 1Password icon, then on the gear and select the option to completely exit)
- Uninstall the 1Password extension from Brave
- Quit Brave with ⌘Q
- Open Brave and reinstall the extension from here
- Quit Brave with ⌘Q
- Finally, open the 1Password desktop app and Brave
Good luck!