These are the steps to access your Windows instance using VNC. I am assuming that you have the necessary permissions and that the network allows traffic on port 443. The details can be found in the Oracle documentation.
Create a local connection:
This is an example:
Start-Job { Echo N | plink.exe -i C:\SSHKeys\ssh-privatekey.ppk -N -ssh -P 443 -l ocid1.instanceconsoleconnection.oc1.us-chicago-1.anxxeljras4jybackio75le7wjglf6fxxxxx -L 5905:ocid1.instance.oc1.us-chicago-1.anxxeljras4xxxxx:5905 instance-console.us-chicago-1.oci.oraclecloud.com }; sleep 5; plink.exe -i C:\SSHKeys\ssh-privatekey.ppk -N -L 5900:localhost:5900 -P 5905 localhost -l ocid1.instance.oc1.us-chicago-1.axxxxxxxxxxxxxxxa
Your private key must be in PPK format. You can use PuTTYgen to convert the key.
VNC viewer:
Bonus: It is possible to use SAC (Special Administration Console). It is disabled by default, but you can enable it using bcdedit:
Copy the command and connect. After the connection is established, start a session and connect to it (example below: session 1). You can type "cmd" to create the first session, and it's possible to have multiple sessions.
SAC>ch -si 1:
Done: