I am not able to replicate this issue. I can produce an error of " gpg: public key decryption failed: End of file gpg: decryption failed: No secret key" if Stored Key Input Mode is not set to Button Press Required.
I set up a new OnlyKey, used the method described above to generate key with GPG and load to OnlyKey. Here is the public and private test key:
-----BEGIN PGP PUBLIC KEY BLOCK-----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=R0qg
-----END PGP PUBLIC KEY BLOCK-----
-----BEGIN PGP PRIVATE KEY BLOCK-----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=Snwn
-----END PGP PRIVATE KEY BLOCK-----
passphrase bob
I load this key through the OnlyKey app like this:
After key is loaded I run this command:
$ rm -rf /Users/t/.gnupg/trezor && onlykey-gpg init “bob@protonmail.com” -sk 102 -dk 101 -i testpub.asc && echo “secret message” | gpg2 --encrypt -r “bob@protonmail.com” | gpg2 --decrypt
…
sec ed25519 2021-03-23 [SC]
04C64623EA51A3B79658DBF7FFADEA1DA23333FD
uid [ultimate] Bob Smith bob@protonmail.com
ssb cv25519 2021-03-23 [E]
gpg: encrypted with 256-bit ECDH key, ID 4B433249E7DE1630, created 2021-03-23
“Bob Smith bob@protonmail.com”
secret message