It’s not a translation, it’s an original English publication that was submitted to Manga plus creators, where anyone can submit to (so it’s an amateur work)

It’s in the official app but it’s in a dedicated “creators” category to separate it from the actual licensed works.

Great to see another mystery club fan. That manga is what keeps me going every week. If you enjoyed that, you should definitely check out the author’s previous work Ika Musume which has the exact same formula.