there's a huge overlap, i transitioned my journal into PKMS. but i still refer to it as my 'diary' as at the end of the day the goal is to write everyday's everything there. the difference is why i write it, previously i used notes as a diary and wrote things to just reflect on the day and then never look at it again. now 5 years later, i write with the intention of linking it to events and things i will be looking at often. like 'i went jogging today' where i take a look at 'jogging' through the entire journal ever so often to see how things are going there (though my goal is to figure out how to make automatic graphs from these kind of things as well).
the bigger difference overtime has been that i eventually merged everything i wrote anywhere into one single linked thing (i use logseq). so notes about work? notes about this random website or pdf? rules and regulation for a thing i do? essays i write? all are interlinked into a single place. the question goes, is this better? and the answer is yes. But I've yet to add all the years and years long stuff i wrote in so many places into it, im glad that future me will have most of my stuff from now on in one place but current me is stressed to find every note i wrote in random apps to paste it into logseq