I checked that royalts 7 beta version supports ssh ca certificate through putty plugin.
However, you need to specify the CA CERT KEY in SSH Advance Options for each registered server, and the KEY must be in PPK format.
This is not a format that can be registered in credentials.
But if you can specify windows ssh client as a plugin, then you can solve this problem.
The mac os iterm plugin specifies the ca cert private key in the credentials, then the ssh client will automatically find the -cert.pub file with the same name as the private key.
Prepare a CA CERTED file inside the same directory.
If you specify only id_rsa in the credential, the ssh client will find id_rsa-cert.pub by itself and send it to the server to try to authenticate with ca cert.
The reason this happens is because the iterm plugin ssh client is a mac os ssh client.
you can install ssh client on windows
If you can specify windows ssh client as ssh plugin, you can use ssh ca cert authentication conveniently.
In Windows users can also install Git Bash which has Openssh. If the feature requested above is implemented, it would be great if the Git Bash openssh was also supported.
The ssh client version included in git bash is 9.0 or later.
SSH CLIENT version 7 or later should have no problem performing SSH CA authentication.
I have verified that there is no problem with SSH CA authentication in git bash.
You can try to integrate other ssh clients using the External Application connection type: