This guide will tell you how to turn on Auto Loot in Diablo Immortal. You just have to follow the simple instructions to do so.
You will need to open up your menu and then go to settings. Go to General and scroll down to “Auto Pick Up Items”. By default, these all are turned off.
There are three options normal, rare, and magic, you have to turn on magic and rare.

But in the early game, you have to get the common loot. So in the early stages, you also have to keep the Normal on.