You can create a shortcut that prompts you for text input, then appends the current datetime, and saves it to the health metric of your choice. You then export this to your home screen.

So when you get good data for your VO2Max (or anything else, really), you can easily save it and look at it on the Apple Health graphs.

The only way to get the Watch to stop messing it up with its daily hallucinated number is to turn off all fitness tracking (in the Privacy settings of all places).

But then half the reason for having the watch goes away.