For an app claiming end-to-end encryption, what evidence would earn your trust?

The only truly-trustable option is basically F-Droid's reproducible builds (or similar) with source code availability:

https://f-droid.org/docs/Reproducible_Builds/

Eg this app: https://verification.f-droid.org/packages/com.inspiredandroi...

and its source code: https://github.com/SimonSchubert/Kai/tree/main

You can verify yourself what it is doing, and what was built is guaranteed not to be tampered with.

AFAIK there isn't any evidence that isn't variations of "trust me bro" for the Play Store and App Store.

"decrypt" button