I have a Linux/Programming/Tech Career YouTube channel (
https://youtube.com/c/tutorialinux ) that just hit 50k subscribers (yay!), and it makes around $450/month in ad revenue.
I also made a poorly targeted and marketed practical system administration Udemy course last year, which does about $500/month.
These projects, along with a few other small things, are on track to make around $15k this year. That's after about 3 years of putting lots of time, effort, and love into creating content on YouTube.
Unfortunately that 'passive' income just barely approaches 10% of what I make at my full-time job (Sysadmin/Ops/Automation/DevOps? stuff), so the idea of working on my 'passive/hobby' projects full-time is not an attractive proposition yet.
I like building, running, and automating large distributed systems, so I'm not really itching to quit my full-time work and "just" be a teacher. The ideal situation would be 'regular' IT work 3 days a week, and working on YouTube, my own web apps, and additional tech courses the rest of the time.