Not trying to make the choice harder, but mailbox.org seems to fit into the choices as well (also hostesd in Germany). Also in terms of hosting in Switzerland, keep in mind that it’s not actually part of the EU, which is the primary/original source for many of the privacy laws you probably care about if you’re looking into these providers.
Since you’re specifically looking to replace OneNote, you might want to take a look at BookStack. It has similar organizational concepts, and I think it’s FOSS.