What exactly are you looking for that ktor might/should solve?
In the OAuth2 PKCE flow you have basically four steps:
1. Generate your PKCE required values (no need for ktor?)
2. Open the authorization page of the IDP including your required parameters (no need for ktor?)
3. Based on the authorization redirect result, call the endpoint for the token (yes, definitely ktor, but this is a simple HTTP call)
4. Use that resulting token for your future requests (yes, enjoy ktor here too)
Do you have specific questions on one of those steps?
If you are looking for a component in ktor client that just takes a configuration and performs all those steps for you, i think thats a no