Sync - On iOS, you can use iCloud to sync your files between your Mac and iPhone. I imagine that there are more configuration options for this on Android.
Publish - lots of different ways to deploy your notes to a site. There's one repo that helps you publish with Mkdocs [1], and I'm sure there are other tools the community has created to solve this problem.
It may not be as simple to set up as Notion, but that's the price you pay for wanting a solution to be cheap, private, and let you own your own data.
