I saw the tutorial and followed it, but step 4, attachments can be found in the zotero database, but not on webdav, I don't know why

Step 5 explains what to do if the file isn't on your WebDAV server.

That's from iOS. That's totally irrelevant, as the page explains, since the file isn't on the server to begin with. You'll need to follow the steps precisely. It asks for a Debug ID for a specific action from the device where the file actually exists.

Sorry, we're not able to help you if you can't follow the debugging instructions we provide. You can ask someone you know to help you go through them and provide the requested information, but there's nothing more we can do for you without it.

(3)(+0000001): Skipped libraries:

(3)(+0000000): [
"0": 1
]

You've disabled syncing for My Library altogether, so you wouldn't be getting new data or files online. See Step 4 here:

https://www.zotero.org/support/kb/changes_not_syncing

Right, you have syncing for My Library disabled.

Thank you very much! Problem solved!