@Coffee That would certainly be useful, but even with the absence of such a feature in the forum, you can still use AI tools externally to help you get to a solution.
I used the free ChatGPT AI Chatbot which is built into Firefox to have a conversation about your issue, and managed to get to the same answer as Laurent proposed (contact your Nextcloud provider) with a logical series of prompts
Prompt 1: For Joplin, how do I solve error "PUT info.json: “/…/info.json” is locked, existing lock on file"?
Prompt 2 (in response to a question): Nextcloud
Prompt 3: How I fix this if I am using a managed instance of Nextcloud?
Here is the full transcript: For Joplin, how do I solve error "PUT info.json: “/…/info.json” is locked, exist - Pastebin.com