If possible, please try this in practice:

create a vault or backup file then attempt to break or extract data from it without the master password

I’m particularly interested in attacks on user-created database/backup files.

Pay the developer enough to take over distribution, add a backdoor, deploy as part of the next update.

Alternatively, use threats of physical violence, including from the government, or appeal to the developer's patriotism, greed, nobility, etc., to install that backdoor.