Different Fitness Goals for different days

Agreed exactly! I have been wearing the Apple Watch almost everyday for nearly 8 years now since Day 1 release and I just realized or figured out yet again that part of your expected daily routine using the Activity app on both the Watch and corresponding iPhone follows just like this: once you wake up or start your day and put your Watch onto your wrist, you should immediately set your Move, Exercise, and Stand goals that you intend to carry out for that day. Later if you see that it is necessary adjust your goals once or a few more times to whichever makes sense for that particular day.

See this as a feature request from us to create an Activity goal schedule somewhere in the app so we can plan our weekdays accordingly to accommodate us. Also the button to Change Move Goal is less obvious than it perhaps should be, so Apple could take this a step further and redesign the Move ring to make it interactive so you can turn the dial up or down on your goals retroactively during your day or even on a previous day. This could be complete with a smart suggestion for the user for what they should aim to accomplish, say an Apple Card-like payment but for calories instead of credit.

You can manually change your goals. Scroll down to the "Change your goals" paragraph:

Track daily activity with Apple Watch - Apple Support

If that doesn't suffice, fill out and submit this form:

Feedback - Watch - Apple