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You should check out Session. Their CTO apparently uses his PGP key to sign every release https://twitter.com/session_app/status/1514108746854985730

If you, as a user, are concerned about reproducibility, you are no longer an average user. Thus, if you want this extra security, you can be expected to check the APK on your phone.

Not perfect chain of custody but could report to virustotal (virustotal.com) and compare in a sandbox:

https://play.google.com/store/apps/details?id=com.funnycat.v...

Maybe you could figure this out yourself, and share your findings, rather than demanding answers from others?

Reproducible builds benefit the user by allowing independent checks of the software.