OpenPGP standard RFC 9580 does not recommend generating RSA keys because RSA algorithm in OpenPGP uses padding scheme that is not considered best practice nowadays:
This is not going to be fixed because there are mandatory to implement Ed25519/X25519 algorithms which are easier to implement and are faster. For “more security” there are Ed448/X448 algorithms which are currently not supported in Delta Chat because there is no ready-to-use implementation. In any case, Delta Chat will likely to stick with Ed25519/X25519 until PQC algorithms are standardized.