Man, I spent way too long hunting for this last year. The most reliable spot I found was the Manga Plus app by Shueisha. It's their official global platform, so the translation is legit and you're supporting the creators directly. The catch is they use a simulpub model—new chapters drop for free when they release in Japan, but older ones get locked behind a paywall or require you to use 'passes.' For 'Jigokuraku' specifically, I think all chapters are available, but you might need to unlock the later ones.
If you're like me and prefer reading on a bigger screen, their website works fine too. The UI isn't the flashiest, but it gets the job done. I've heard some folks swear by the Shonen Jump app, but I believe the content library is pretty much identical. The biggest upside is no sketchy pop-ups or malware risks, which is a relief after wrestling with some of those ad-heavy aggregator sites.
Honestly, the official translation quality is worth it. The terminology and nuances in a series like this, with all its historical and mystical elements, can get butchered on fan sites. I started on one of those and then re-read it on Manga Plus; the difference in clarity, especially for the esoteric Taoist stuff, was night and day. You just have to be okay with reading in a browser or their dedicated app.