If I've tried everything else, is there anything else I can do about Destiny 2 'Guitar' errors?

If you've exhausted all troubleshooting steps, including contacting your ISP and ensuring Destiny 2's servers are stable, consider contacting Bungie's support directly. Provide them with detailed information about your network setup, the frequency of the errors, and any troubleshooting steps you've already taken. They may be able to offer further assistance or identify underlying issues on their end.