Is there a way to adjust Apple Watch's fall detection sensitivity?

And to answer your specific question, no, there's no adjustment, just on or off. If you confirm that Fall Detection is on, you may want to contact Apple Support and discuss the issue with them. There may be a problem with the hardware in your Watch that should detect falls.

Regards.

hello bobbwhit welcome to Apple community I see here that your Apple Watch fall detection isn’t working have you made sure it was always on and not for workouts here is a link to apples website about fall detection Use Fall Detection with Apple Watch – Apple Support (AU)