Hi Andy,
Click on the form and in the right hand-side panel scroll to ‘dynamic events’ click on that - then click on ‘server connect’. You’ll see the types of responses you can create events based on. I’m not sure which one specifically relates to the catchall 500 error, maybe just ‘Error’ but you could select that - and then use that event to trigger an alert on the form to let the user know something went wrong.
Matt