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…)
If you’re just worried about people you live with and passive scan type stuff I’d do a LUKS flash drive and a txt file. If you are worried about more active stuff from 3 letters then I still think digital is going to be the best bet, but you’d better use qubes or even dedicate an airgapped computer with an encrypted drive but even that is iffy for a serious anti gov threat model.