I’m on an iPhone XR and can’t replicate the slow dictation in German. It is about 1-2 words behind even when I’m dictating quickly. Are you on 17.0.1 already? The update fixed battery drain and heating issues for me. I assume something was not quite right after updating to 17 on my phone and the .1 update fixed it.
As someone commented already you can use a personal automation to trigger when you leave a specific location. In case you are using a focus mode for work (which can be location and/or time based) you can use the activation and deactivation of this focus mode to trigger an automation as well!