I’m the author of SilentNotes, a note taking app with privacy in mind. I think it would be a good fit for this site because it shares the same goals, but I’m unsure whether this is the right way to ask.
SilentNotes can share the notes between Android and Windows devices, but it does it end-to-end encrypted. The notes can be written in a WYSIWYG editor with basic formatting like headers or lists and they can be self-hosted. SilentNotes is an open-source project, its source can be found at GitHub.