While I would use a PIN lock, I don't expect it will ever be supported.
- The related Github issue has been locked since 2019.
- The related FAQ entry has existed since at least 2023.
- Even Google apparently provides an answer stating Joplin does not have local or at-rest encryption.
Yet, PIN lock continues to be requested countless times in this forum for years now. The last request was made just a few days ago.
All this is either insufficient or unseen before users submit requests for a PIN lock. Do users typing "PIN" into a new topic need to be forced to read the above resources before posting?
If you need PIN lock, I'm convinced that you should use a different notebook app which supports it (like Notesnook or Standard Notes), a separate app locker, or develop the feature yourself.