Apple Magic Trackpad way too sensitive

While you do that please review this old, obsolete Apple Support document: If your pointer is jumpy when you use a trackpad, Magic Trackpad, or Magic Mouse - Apple Support (Archived). It includes the recommendation to try "Safe Mode".

I do not know the reason that document was removed. The recommendations in it are sound, with the possible exception of its recommendation to use a Teflon appliqué which seems dubious to me.

I can personally verify third party power adapters can also be a causal factor. Determine if the problem exists only while your portable Mac is connected to a power adapter (genuine Apple or not) and subsides when unplugged. If it does, that would be definitive indication the power adapter and / or its cable may be at fault. Another, even older Apple Support document discusses that possibility: Intel-based Apple Portables: Troubleshooting unresponsive trackpad issues - Apple Support (Archived).

Other factors such as skin chemistry can also cause bizarre problems. It could conceivably be related to the use of hand creams or soaps or even perfume, which that archived Apple Support document described as "oils or lotions". For example I strongly suspect that's one reason some people have such awful experiences with Apple's white USB and power cords while mine remain pristine and intact even after a decade of daily use.

Let me know what you determine, because the next step would be to have that Mac evaluated by Apple.

That's possible. Consider the possibility of Bluetooth interference: Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support

And don't use rechargeable batteries; they won't work. Use good quality alkaline batteries.

For reference: If you can't connect your Magic Keyboard, Magic Mouse, or Magic Trackpad to your Mac - Apple Support. That's about all Apple has had to say on the subject recently.

You might try "forgetting" or un-pairing the Magic Trackpad (yours is now known as the "Magic Trackpad 1" to distinguish it from the current production model) followed by pairing it again: Set up your Magic Keyboard, Magic Mouse, or Magic Trackpad with your Mac - Apple Support

Please determine if the same problems occur in "Safe Mode": Use safe mode on your Mac - Apple Support.