[JavaScript Error: "'777NN0XM' is not a valid item key" {file: "chrome://zotero/content/xpcom/sync/syncEngine.js" line: 0}]

You used some plugin or AI tool that created local items with invalid keys that can't sync. You'll need to 1) contact the tool developer and ask them to fix it and to fix your database, 2) identify the items and delete them (and empty the trash), or 3) delete your database and sync to pull down your online library. I'm afraid we can't help with this.