Hello elina7,
Welcome to the Apple Support Communities. I understand you're finding your cursor seems to intermittently disappear.
For confirmation, has this ever happened when you're not using full screen mode or another monitor? Or only under those circumstances?
I'm wondering if the cursor may actually be moving on its own rather than disappearing; I recommend starting by trying these steps to help rule that out, including testing in safe mode: If your pointer is jumpy when you use a trackpad, Magic Trackpad, or Magic Mouse.
As another test, I recommend clicking Apple menu () > System Preferences > Accessibility, and then clicking Display in the left-hand column. Then, check the box next to "Shake mouse pointer to locate." The next time the cursor disappears, try moving your trackpad or mouse back and forth quickly to see if the cursor appears without needing to right-click. Knowing how this works would help narrow things down a bit.
I hope this gets you started!
Take care.