Solution:
By default, Rosetta 2 is not enabled in macOS 27!
It was enabled in macOS 26, which is why this issue didn't exist there.
Rosetta 2 is included in macOS 27, it's just not activated by default 😉
So, you need to activate Rosetta 2 in macOS 27 using a Terminal command.
https://support.apple.com/en-us/102527
scroll down the Apple website, and you'll find what you need at the very bottom.
It is not the case that Rosetta will be used when running the native Steam-client or a native game; every native game runs without using Rosetta!
The reason you still need to enable Rosetta 2 is that the native Steam-client checks by default whether Rosetta 2 is available at all, ensuring you have the option to play non-native games as well.
If the Steam client cannot address Rosetta on your Mac, it will interrupt the game startup!
This compatibility check occurs by default every time a game is launched (for any game!).
So you can safely activate Rosetta 2 and still be sure that, as long as you play native games, it will never be used.
I checked this on my system, of course.
This query from the Steam client is made solely to give you the opportunity to play intel-based games as well.
Keep in mind...
macOS 27 (Golden Gate) will be the last release of macOS to fully support Rosetta. That means that from macOS 28, apps requiring Rosetta will not work!
Hopefully, Steam is already working on disabling this pointless prompt for native games!
I write "hopefully"... because Steam obviously doesn't care about Apple users... How long did it take them to release a native Steam client,... and it's still in beta......
. It shows no access is given.
