There is difference with free software and proprietary software. NextCloud instance is free software and holds encrypted information. Maybe there could be ways to intercept password by the ISP.

This application is proprietary software, and you don't know nothing what is going on in background. Just as majority of Service as a Software Substitute, or SaaSS steal people's data.

See: https://www.gnu.org/philosophy/who-does-that-server-really-s...

There are torrents with information to download with all details of many major websites. It means NO SECURITY.

So if I a stranger from street asks you to give him your notes, you won't give him. But you see him face to face.

If a faceless guy online, which you don't know where is he located, asks you to give him all your notes, you even pay to him to give him.