There is no way to be 100% sure, but:
- bitwarden and ente have open source clients that ecrypt all data locally in a way that the provider can’t restore data
- nextcloud isn’t optimal, while you can encypt data at rest, the provider might be able to spy on you
- With mail providers it is difficult, but mailbox.org has my (personal) trust by building their business model on data protection and open source
That’s true, but might not really be a problem for most. Just set the jail time to something short (few minutes, maybe an hour).