“To this day I did not succeed in finding a combination that satisfies all my requirements, aside from notes using WebDAV+Joplin.”
CalDAV has been a standard for over a decade, and he still couldn’t find clients that work across Windows, Mac, Linux and iOS. The polished apps keep your data in their own silo. So after weeks of testing he is back on Google Calendar and Todoist. Open standards lose when nobody funds the boring libraries that make them usable.