If you want something self-hosted look into Foam[0]. You write your notes in VS Code with Markdown. Many web frameworks can then generate interactive sites from it.
(/s, referencing https://news.ycombinator.com/item?id=8863)
This looks very hackable too (in the good way).
If they created an open source version I could self-host, I would happily adopt it. Frankly it looks beautiful and is only missing easy file integration. But they don't because it would cause them to lose a vast source of value they provide to their customers (providing proxies and servers for people to access their data remotely).
The only part of their business model you can't go around is the fact that they're not FOSS, and for business use you need a business license. I personally find the terms quite acceptable (only apply if you work in a for profit place with more than two employees and more than X revenue), and the price is good value for money for me.
So where are these anti-user features? Why does the business model lead to them? "Not open source" doesn't count.
FOSS allows you to choose to be free tier or pay for their services. The difference is in the free tier: you can do the leg work and hack together your own systems to match their paid services (namely public hosting). Its sort of a promise that you can use, audit, help improve, and love the free product without having to be concerned about forfeiting your privacy or security.
Additionally, FOSS projects always benefit from community auditing of the code, increasing the reliability and security of the software instead of relying on a few individuals to catch bugs.
Anyways all this to say "not FOSS" might not count itself, but implies there are other anti-user features at play.
Outside investors seem to me to be the real anti-user signal. Everything else flows from that.