The FIPS specified a "legacy mode", which is up to the application to decide. In this mode, usage of RSA keys of size 1024b, 1280b, 1536b, and 1792b should be allowed only for verification.
In addition, I would like to re-raise the issue if it would make sense to limit RSA key size generation and usage generally (previously mentioned in https://dev.gnupg.org/T5512#151635). Right now, there are no lower bounds for RSA key usage and tests happily use many 512b RSA keys. My suggestion would be to allow only 1024 bits and larger by default. The change is also attached in the following merge request as well as in attachment here.