I took the JLPT purely for self-enrichment too. didn't require it for work or for school or even socially. I just wanted to have that feeling of achievement hahaha
I went for Ikoma's prep course for both N2 and N1. For the other grades, I think it's possible to self study them, but I never took those exams because I felt it was a waste of money.
If you purely want to pass the JLPT, i think Ikoma's prep courses are very good. They give you these incredible notes and the mock tests are similar so you really get the practice and info needed. But on the flip side you hardly talk in there beyond the initial introduction in the first lesson, so if you were looking more to be able to talk, then you might want to consider their other courses.
Good luck for the JLPT! It made me quite happy when I passed it and received the cert, so even if it's not for any official purpose, if you want to do it, I encourage you to attempt it!!

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