Maybe interesting is the evolution of my system:
• 2015 and prior: Sticky notes, calendars, notebooks, sheets of paper, chaos
• 2016-2019: I found the bullet journal method and implemented the most basic form found here: https://bulletjournal.com/blogs/faq (collections, future log, monthly log, daily log) and never really evolved from that utilitarian mode.
• 2019-2025: I signed up for Notion and ported my bullet journal system there. I miss the physical version, but prefer the easy access and easy editing in the online version. In addition to Notion, I heavily use Google Calendar, and also Google Keep as a quicker-access and catch-all of smaller notes. I use Notion for life admin and Obsidian for work notes and files.
OP's Johnny.Decimal system caught my attention since I've been interested in a consistent and proven way to organize the files on my laptop, SSDs, Drive, as well as all my physical docs. I could also see it being a nice way to organize my Notion and Obsidian, but I also tend to rely on search and backlinking as others have commented about for their own systems.