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I am having a LOT of trouble controlling the camera with a mouse. I've turned the sensitivity all the way down, but the slightest movement spins it around like a gyroscope. Is there some degree of control I'm missing? It took me 10 minutes to walk across a field!!!!
That sounds an awful lot like I bug I've experienced when playing Subnautica on linux through both steam's proton and regular wine. Any chance you are on linux? If so, one workaround in the Subnautica version was to alt-tab out and back into the game whenever it starts doing that; however in some cases that would cause the mouse pointer to be locked in the center of the screen when attempting to interact with menus -- another alt-tab toggles to the mouse-works-in-menus-but-not-for-camera mode. In the regular wine attempt, I was able to seemingly eliminate this issue by enabling wine's virtual desktop emulation (set to the same dimensions as my monitor's native resolution), but for some reason that didn't work in proton.

If I'm wrong and you aren't using wine, sorry for the useless information. :) Good luck with your problem!
This FAQ was of some help.

Try disabling the Enhance pointer precision option. To do this, please follow these steps:

Windows 10:
Press WinKey+R, and in the Run window type:
After that press Ok, and navigate to Mouse -> Pointer Options, then make sure that Enhance pointer precision is unchecked, and click OK.

Windows 8.1, 7:
Start -> Control Panel -> Mouse -> Pointer Options, then make sure that Enhance pointer precision is unchecked, and click OK."

This alleviated the problem--at least now smaller movements control the camera reasonably well--but it still spins wildly if you go too fast.