Hi @toad78
I believe you can do it by using custom JS code. In the JS code, you can check if the selected choice is 1-column and then change the text editor width. You can add the script by using the acf/input/admin_footer action hook. Please take a look at this page to learn how to add custom JS script: https://www.advancedcustomfields.com/resources/adding-custom-javascript-fields/.
I hope this helps 🙂