I'm investigating GnuPG v5 functionality, so modified GnuPG sources to always generate a v5 keys. This works (including using generated keys with GnuPG 2.4.0), however attempt to export non-encrypted secret key fails, producing the following packet dump for RSA key:
```
# off=0 ctb=95 tag=5 hlen=3 plen=2921
:secret key packet:
version 5, algo 1, created 1686657810, expires 0, pkbytes 391
pkey[0]: [3072 bits]
pkey[1]: [17 bits]
protbytes: 0
skbytes: 201210263
skey[2]: [MPI_NULL]
skey[3]: [2685 bits]
skey[4]: [MPI_NULL]
skey[5]: [MPI_NULL]
# off=2924 ctb=b4 tag=13 hlen=2 plen=6
:user ID packet: "v5_rsa"
```
For encrypted secret key export/import back works well.