EntraID + F5 as Oauth client/resource server not sending ID Token to app

In order to validate the token tou need the JWT key
F5 fetched jwt keys when you created the oauth provider, note that jwt keys are rotating so you need to create a scedule in F5 to look for new keys
Therefore even in jwt.io you need to provide the key in order to validate token

As for .default scope i have never used it, I will have a look

Have you configured your web app as resource server?

And if yes are you using same credentials as on F5?