Hi @coughlin
I hope you are doing well.
Our developers confirmed it needs custom coding, we do have a code created for a different situation that can work here
Could you please try this link https://gist.github.com/wpmudev-sls/5be7b5f7eac4132e1539b850b8ab751c as a mu-plugin?
You can find how to install a mu-plugin on:
https://wpmudev.com/docs/using-wordpress/installing-wordpress-plugins/#installing-mu-plugins
To use this we need to update the code at some lines.
In line 47, add the form ID that you would like to apply the code, you can find the ID in the URL.
https://monosnap.com/file/Y6wgDNUqMeJfa1H75qAFgM45Qftxpz
Line 48, add your Select field ID and the number of option you would like to allow the user, on your case it is 1, it must be a multi-select field, edit the field and add this class on your custom class setting:
wpmudev-option-limit
https://monosnap.com/file/4ph5sSrhtZ6YtuADZey9UfUzOZ0eQM
https://monosnap.com/file/qtR1sSBZI52G3eHlMW89pAUxG21D6q
The result:
https://monosnap.com/file/ocuniSARYLUtQfQP7tNzWyjIC4l3Kt
Let us know if this workaround will work.
Best Regards
Patrick Freitas