There is no "lock". Your own library is personal and private. If you want to share references with others (read-only or read & write), use groups: https://www.zotero.org/support/groups
The citations are locked in my group library and others cannot access them to edit them further. There is a lock symbol next to group members names - for annotations that they create in the document in Zotero.
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If you want to share references with others (read-only or read & write), use groups: https://www.zotero.org/support/groups