Hi,

There is an upcoming botan3 transition to version 3.13.0+dfsg-1, as
available from experimental.
Your package currently builds with it, but some of its self-tests are
failing. What I know is that OpenPGP MPIs have leading zero bytes
stripped, so about 1/256 of RSA ciphertexts and signatures is one byte
shorter than the modulus.
Botan 3.13+ rejects such inputs and that's why upstream tests need to
be adapted. Your upstream seems to have this fixed [1], but I can't be
sure as the issue itself is not yet closed.

Regards,
Laszlo/GCS
[1] https://github.com/rnpgp/rnp/issues/2465