Unfortunately, location based Automations require user to respond.
Can create/use a Focus. Specifically the Fitness Focus (or create a different one if you want to). Set a location in there. And if on iOS 16, can specify which Watch face to use. Focuses do not require responses.
Or can create an Automation that triggers when a Workout starts and have that switch faces. And have a corresponding Automation for when Workout ends. These too will run automatically.
EDIT: for anyone that stumbles upon this thread, it appears that iOS 17 will have location based Automations that do not require user response, so above, while still valid, is not the only method. Can simply use location Automation.