I am sorry to hear this Afronomist! Surprisingly you already should have an app on your macOS that does what you need. The Apple Notes app is amazing and has great security. You have the option to "Lock" your notes I already use this feature and it protects my most important data with my custom password. Here are some instructions directly from Apple Support below:

iPhone and iPad:

https://support.apple.com/en-us/HT205794

macOS Sonoma: (at the top of this article you can change the macOS thanks) https://support.apple.com/guide/notes/lock-your-notes-not28c5f5468/mac

Extra option: I would also like to suggest an Anti-Virus system as well for your macOS. Mac is secure with Gatekeeper and SIP and everything but with anti-virus system it might help to protect your Mac even more. Malwarebytes, Kaspersky, and Bitdefender are pretty good ones to name a few.

I hope you the best Afronomist and I hope this helps my friend.