I don’t there’s any blessed way to do this. Turbo Drive will add a header to accept a turbo stream when you submit a form. If you have this header, Rails will trigger your format.turbo_stream block and not format.html.
To get around this, you could turn turbo off for that form by adding a data-turbo="false" attribute. Or you could include something in the form itself — I’m thinking a hidden input — that you can pick up with an if/else block in your controller.