I can’t use pen and paper because I’m surrounded by nosy people who don’t know to respect my privacy. And if I put some kind of lock on a physical diary or something, they complain that I am hiding something.
Establish limits and set boundaries, if you have to. If that means a locked room, desk, trunk, or other means, then do that. Often the best way to establish boundaries is to assert them.
You situation sounds intrinsically toxic. I understand you're married with family --- if that's where the privacy issues are (rather than at work), you might want to consider family counseling. A lack of basic trust or respect is a bad sign.
Meantime, digital encrypted systems may be more appropriate, though personal notations and code can help with paper --- you're not the first person to have nosy neighbours.
Reasonable or not, one difficulty I have with keeping any kind of journal is that I keep thinking of the fact that it may eventually be read and exposed to the cruelest, least charitable interpretation.