This is probably one for a Postman Employee to respond to.
But I suspect this will need to be a feature request raised on the Postman Github.
You can add a parameter (if needed) under the advanced settings to return an ID and Access token if the endpoint supports it, but as you have found out, you can only set one or the other to a variable, which doesn’t help if you need both values.
The feature to allow you to select between the tokens was only implemented last year.
This relates to your previous question.
Salesforce OAuth2 id token - 
Just Getting Started - Postman Community
I would recommend a feature request that allows you to map the auth response to a variable in its entirety which you can then parse and access the various elements within. (Rather than individual key\values). This would give more flexibility and access to all of the auth data.