You're running a version of Zotero from January 2019. It should say "This version of Zotero is too old to sync. Please upgrade to a current version to continue syncing." if you click on the sync error icon.
You'll need to install Zotero 6 from the download page in order to sync, and you should figure out why you haven't received automatic updates in several years.
You'll need to install Zotero 6 from the download page in order to sync, and you should figure out why you haven't received automatic updates in several years.