It used to work that way… then Samsung replaced the old integration with this current version, which forces the user to share every device with Amazon and/or Google. I would not hold my breath for this feature ever returning, as the last time I saw anyone from Samsung mention it was back in January, roughly eleven months ago.
Initially stated the work began back in August, 2020…
And then mentioned that it was still being worked on in January, 2021…
I have not noticed any official word in the community from Samsung since then.
I do not believe Amazon has an official API to allow this type of integration. It used to be possible via a Community Integration called Echo Speaks, but Samsung pulled the plug on that as well due to excessive cloud server usage.
There are other platforms that allow individual device selection for Amazon Alexa and Google Home, and that can run Echo Speaks, if these are important features for your requirements.