Solved. After a bit more playing around I finally figured it out.
In the Configuration for XOA set the following in the "AutoDiscovery URL" https://{Yourdomainname}.okta.com/.well-known/openid-configuration. Do not fill in any of the Advanced fields. They will work just fine.
Then in OKTA for the 'Sign in' redirect URLs put in the following. https://{Your XO servername}/signin/oidc/callback if you access the server through multiple URLs you may need to add additional lines.
Make sure you have the PKCE checkbox turned off or you will get a 500 server error on the client side. The OIDC plugin does not like to use PKCE.
If you choose to have the option of "Login Initiated by" set to either OKTA or App then you will need to set the "Initiate login URI" to be the same as your 'Sign in' redirect. This way you can have your XOA control panel in your list of available SAAS apps in your OKTA browser plugin for authorized users.
Leave off the wildcard checkbox since it just makes you less safe.
This should help anyone else who is not an OIDC expert figure out how to make XOA behave with your OKTA installation, hopefully, this will help out the next person who runs in this challenge.