No, that's not possible — if you delete something online, it will be deleted locally.
The point of Zotero syncing is to make your library available everywhere. You can configure it not to download files onto every device, but everything will always be available in the online library.
The main exception is that if you leave or delete a group, Zotero will ask you whether to keep an archived copy of the group locally (which will never be syncable again). But that's more of a special case, not something to rely on for normal usage.
The point of Zotero syncing is to make your library available everywhere. You can configure it not to download files onto every device, but everything will always be available in the online library.
The main exception is that if you leave or delete a group, Zotero will ask you whether to keep an archived copy of the group locally (which will never be syncable again). But that's more of a special case, not something to rely on for normal usage.