This entire section is FUD. Trust is "Still Required™" - unfortunately HN doesn't support underlines so I can't get accross the full obnoxiousness of the original formatting - therefore having your data in someone elses database is no worse then using an app that someone might add a backdoor to?
It is a very common pattern that an app which claims to be secure turns out not to be. In fact I would say that claim to be secure and actually live up to that are probably the exception rather than the rule.
This is why we self-host 99% of the content related to managing Supernotes (as a business) on Supernotes itself, but (a small minority of) sensitive content we keep in 1Password, which is one of the few apps I trust to have done E2EE well enough for me to feel that data is secure.
This is why I like what the folks over at Notesnook are doing with Vericrypt [0], which essentially allows users to verify the encryption themselves in a very easy to use way.