Out of curiosity, why do you require that? On my desktop, my system account is protected, never left unattended while unlocked, and I've got full-disk encryption.
I can't presently imagine a benefit to an extra password for my notetaking application, so your comment makes me wonder whether I'm missing something or whether I just use it a little differently than you do.
I have other people use my computer from time to time, but not for enough time to warrant a separate account. From what I understand, Joplin's data is also stored unencrypted on disk. I don't use full-disk encryption and I don't want to use it just for Joplin. Are people using my computer going to open up my notes app or snoop around in the sqlite db? Probably not. But I like to have the peace of mind.
I can't presently imagine a benefit to an extra password for my notetaking application, so your comment makes me wonder whether I'm missing something or whether I just use it a little differently than you do.