I had my phone (Huawei P20 lite) in ultra battery saving mode and manually set the light to lowest possible (went hiking for 2 days and tried to save as much battery as possible) and when I tried to use it during the day, everything was so dark I didn't knew what I was pressing.
Since then, I have additional grey "button" on screen, which does...something weird. If I just put finger on it, I can drag it across the screen and leave it wherever I want. But, if I hold my finger on it for ~2 seconds, then it acts like a cursor and if I move it left/right/up/down, it just does same thing as I would press the most right button on the bottom of the phone (square).
How can I disable this "action" or how it is even called? I would take a print screen of the desktop, but the circle isn't shown on it. But here's a drawing, how it looks like.