Why does my mouse pointer jump back and forth when using the touchpad under the Thinkpad L540 when I connect the power supply to a 1500W sine wave inverter?

It's kind of awesome. So far I had a 500W inverter with a square curve and that wasn't a problem. Now I have connected the Thinkpad to a pure sine wave inverter on a trial basis, but the mouse pointer can't be used normally on the touchpad. He jumps back and forth. I also tried it in a live USB Ubuntu and it's even more blatant. The mouse pointer hardly moves at all.

What can that be?

This could have something to do with the ground. The negative pole on the plug of the power supply unit is connected to the protective contact. If you have irritations there, this could possibly affect the capacitive touchpad.

try to ground the inverter and see what happens then.

Can such an inverter break any electrical device without a protective contact?

Normally not directly, but without a protective contact, various protective mechanisms will not work in extreme cases.