I had this same issue and the following solution is much clunkier but at least works for my needs:
Open "Automator" to create an "Application"
Search "shell" and make a new "Run Shell Script" action.
Use this as the script text.
osascript -e 'tell app "Terminal"
do script "arch -x86_64 zsh"
end tell'
Save this application in Applications/ by the name you prefer such as "Terminal (Rosetta)".
You can now drag the Automator application you created, into the dock for quickly launching.
Explanation:
arch -x86_64 zsh command runs zsh as x86_64. You could simply run this from a terminal (and maybe that's where this solution could end, since likely you'll be spamming "arch" command frequently just to make sure you're in the right architecture anyway).
By using Automator you create something Apple will let you drag into the dock for convenient launching.
(I'd rather not have to use it, but as it turns out if you just create a shell script in Applications, you're not allowed to drag that into the dock.)
If you just had arch -x86_64 zsh on its own, Automator doesn't visibly show an interactive terminal window for you interact with, hence extra fluff to launch the separate terminal.
Cons:
Annoying to set up
The "terminal" button will have the Automator robot icon instead of looking like a terminal
After launching this by clicking that icon, the actually open terminal window will be grouped with other terminals rather than grouped under the button you used to launch it
So by extension clicking the icon multiple times just spams more terminal windows open rather than going to what you already had
Sources:
The arch command: https://stackoverflow.com/a/71065637
Using Automator: https://stackoverflow.com/a/281455
Launching separate terminal window: https://superuser.com/a/308460