A paper-only journal would defend against the state, but not against people you live with. A digital journal can be encrypted, but an intelligence agency could potentially gain access (like, them reading your anti-government rants that may involve violence… that sort of stuff).
So… how to defend against both threats?
(Also, I just realized, paper journals cannot really be easily backed up…)
A digital journal doesn’t need to be any more government-accessible than a paper journal.
Depending on your threat model, this could require special hardware, special software, or both. In order of ease of setup, I would suggest:
Keep all your data on your own physical media. No cloud services, period.
Keep it encrypted.
Disable network connectivity at every level that you possibly can, such as:
OS level: disabling wi-fi, disable blutooth, and disable networking entirely.
Firmware/BIOS level: If you BIOS has options to disable networking components (especially wireless ones), do that.
Hardware level: If your laptop has a switch to disable wi-fi, use it. If ethernet, unplug the cable. Etc.
Physical level: Remove any removable wireless cards or antennas.
Wallet level: buy a computer than never had wi-fi or bluetooth in the first place. This could mean a retro computer, or could mean using a micro-pc like some models of Raspberry Pi.