Good morning and great question. There are some really great examples out there like LinkedIn Learning about video content that individuals can access to learn new skills.
I think what you’ll find is that many of those online courses start with work that individuals did for individual clients. Have you tried taking work you may have done for a client already and figure out a way to put it in to a video (or long form per Richard above) content and test it with other clients that never received that training?
It could be a good and easy way to create content and get rapid feedback that you can then use to fine tune your offering. I am sure you have found in your business how frequently you get asked for similar advice.
From there you could market to past clients via a website and then move on to creating your own online presence, etc. .
Hope the above helps.