Correct - the Google and Alexa integration control the ability (or in this case the inability) to filter devices from their respective services. Which version of the app you use has absolutely no bearing on the feature. What you’ve asked for is the #1 most requested feature for all of Smartthings in the last year short of 'go back to Classic!" since the new Alexa and GH integrations were released.
Link to the ‘new SmartThings Alexa Skill’ Megathread - https://community.smartthings.com/t/new-smartthings-alexa-skill-2020/
Yes, I know yours is GH, but it’s basically the same issue. This one has better comms with the dev team on it - look for posts by Blake and Lars for ST responses.