This topic has been raised quite a lot on this forum. It is a bit awkward to search for these topics as "password" is a common term. Searching for something like "PIN Lock" should find a few and it will give you an idea as to the devs reasons behind this decision. This post is an example of the conversations had and also dates from around 2019.
I am not a dev but I believe that the thought is that full disk encryption and not leaving a computer logged in and unattended are far better protection. Adding a password to open the app would only give a pretence of security as your notes would still be stored locally in an unencrypted SQLite database.