Disabling "submit" button when specific value selected on a dropdown field

Hello,

On my ticket creation form, we have a dropdown for product selection.
When customers select our open-source product, I want to point them to our community.
For that to be done, I would like to identify a specific product selection in the dropbox so I can disable the "submit" button in the JS code, but I could not find a way to get the selected data from the dropbox. H

ave any of you ever done that, or would be able to help me?