What counts as a loaded chunk?
Level and load type Levels are numbers that determine what load type the chunk is. Load levels range from 22 to 44 in regular gameplay, while only 22 to 33 are relevant. Load levels less than 22 (including negative levels) are valid but only possible with a modded game. Load levels above 44 are not possible in vanilla.
How far do chunks get loaded?
By default, chunks are loaded around you in a circular shape, with a radius of 10 chunks. So you would need to walk about 160 blocks away for the chunk to be unloaded, and for the items to not despawn.