I write a newsletter on cybersecurity every week. Usually a summary of interesting articles and a list of known breaches and software issues. It's been going for seven years now I think? It makes about 25k in sponsorships each year, although it could be more if I actually got myself to sell a bit more. Either way, it's been a great way for me to keep learning. Nothing beats having to summarize a thing to thousands of people to make sure you really understand it :-) https://securitynewsletter.co