I don't know that Twitter actually needs to be fixed. It's very good for what it is - a microblogging platform that provides instant, timely updates on news and current topics.

I think Twitter could, however, capitalize on its platform and offer additional, successful features. Twitter could offer Patreon and Substack-esque features where users could subscribe to additional, richer, and more in-depth content from content creators. Twitter could also re-explore a live broadcast feature with associated live chat (similar to YouTube and Facebook live broadcasts). Twitter is a huge platform and has plenty of opportunity, but I don't think it suffers from inherent problems like Facebook (which has an aging userbase, users abandoning the platform, and a big spam problem).