(It's a documentation page, not a "thread". If you say "thread", people will think you're referring to some thread in these forums.)
You'll need to explain what the actual problem is and what part of Files Not Syncing you're following. But note that most of your files are linked files, not stored files. From that page:
If Device A is a computer and this is a personal library, make sure the attachment is stored within your Zotero data directory, not linked to a location elsewhere on your disk. Zotero syncs stored files; linked files need to be synced outside of Zotero. Linked files are indicated by a chain in the attachment icon. You can use Tools → Manage Attachments → Convert Linked Files to Stored Files to make the files syncable.
Oh ok. I clicked that button and it converted only one file, so I thought that there was only one linked file. I did not realize I needed to select all files then hit the convert linked files... button. I think that may have fixed it. Thanks for the help!
Upgrade Storage
You'll need to explain what the actual problem is and what part of Files Not Syncing you're following. But note that most of your files are linked files, not stored files. From that page: