Settings → Devices → Touchpad → Touchpad sensitivity → set to "Most sensitive" is wrong direction — set it to "Least sensitive" instead. This stops light/accidental brushes from registering.
Settings → Devices → Touchpad → scroll to "Three-finger gestures" → set to "Nothing" or change from Switch apps/desktops if you don't need it.
Also check "Four-finger gestures" similarly.
Run the Surface Diagnostic Toolkit
Update Touchpad driver.