[mbed-tls] How can I encrypt with a private key?

Hi all, I have been using the old version(2.28) for a very long time, and updated to version 3.4.0 recently. When using rsa encryption, there is a parameter 'mode' that allows to choose whether to use a public key or a private key. Why is it canceled in the new version? And how can I use the private key to perform an encryption operation? Thank you for your help!