Minecraft wiki entry for The_Nether, associated text: Upon entering the Nether as a single player, the passage of time freezes in the Overworld, resuming when the player returns unless the /forceload command is used. This is due to the spawn chunks no longer being ticked, and not chunks loading and unloading as some players believe. The spawn chunks are kept loaded when there are no players in the Overworld, but most stuff other than basic redstone stops working.
The numbers for the 3 dimensions are -1=the Nether, 0=Overworld, 1=the End. This contributes to a misconception that the Nether is "below" the Overworld, although Dinnerbone confirmed that they are simply separate dimensions.[6]
In Bedrock Edition, if a section of the bedrock ceiling is removed (e.g., through commands) mobs can spawn directly below where the ceiling should be, despite the surface density cap in the Nether being 0.
In Legacy Console Edition, the size of the Nether is limited, with bedrock walls surrounding it on all sides. The Overworld-Nether ratio varies depending on the world size: it is 1:3 for Classic and Small worlds, 1:6 for Medium worlds, and 1:8 (the same as Java and Bedrock editions) for Large worlds.
The crimson and warped forest biomes are suggested to decontaminate the Nether environment from potential landfill pollution that coincides with the presence of Ancient Debris, as stated from an article from the official Minecraft website regarding netherite scrap.[7]