If you’re reading fan translations then BakaUpdates is what I would recommend using since it follows the release of scanlators. I believe many scanlators themselves are using some form of email blast or RSS announcement of new chapters as well. I don’t doubt some use something like Discord to announce releases, but that’s not a preferred method for me to hear about releases. You’re welcome!

That’s a good question. I imagine the publisher’s office would have updates listed for serialized manga. I wouldn’t be surprised if there is an RSS feed or something similar out there for official updates. I think sites like MyAnimeList would list official releases. I use BakaUpdates, but that’s not following the serialized release schedule. I hope this helps!