An extremely simple mob switch consisting of a silverfish spawner, a trap, and a chunk loader. Any mob in a lazy chunk is not processed, so they do not despawn. This approach allows for great variety of mob switch possibilities that extends far beyond the 4 types of mobs that are normally used (zombified villagers that have been previously traded with, shulkers, withers, and wardens). Another 4 mob switch designs are included and discussed in the video.

This mob switch is designed for vanilla and may not work on modified servers that have different lazy loading mechanics and chunk loading mechanics. Be sure to read the NOTE for 10:06 below.

IanXO4 discord server:   / discord  
WDL with 5 mob switch designs: https://www.mediafire.com/file/lrb0w9...

REFERENCES:
https://strongholdfinder.com/
https://www.chunkbase.com/
Mercury's Chunk Loader: https://www.bilibili.com/video/BV17M4...
Dark's Chunk Loader v2:    • The Simplest Chunkloader v2  
Instant Shulker Farm:    • Minecraft Elegance: Instant Shulker F...  
ilmango's warden overworld mob switch:    • Warden Mob Switch 1.19  

0:00 Intro to Mob Switches
0:27 Material List
2:05 Chunk Loading Levels
4:52 Selection of Stronghold Build Site
5:27 Build Tutorial
9:18 Stocking the Mob Switch, READ NOTES IN DESCRIPTION
10:18 Instructions for Use
10:59 4 Mob Switch Examples in WDL
12:24 Outro
13:33 WDL Commentary

NOTES:
2:05 A Minecraft world isn't actually infinite, but it is exceptionally large, at about 1 quintillion cubic meters of buildable space per dimension. Players can also travel above the build limit, with occupiable space of about 10^32 cubic meters per dimension.
10:06 Some servers have a slight delay in unloading the stronghold when you teleport away, which may cause the silverfish to despawn if there are other players in the overworld. To fix this issue, leave the stronghold through the chunk loader portal only when no other players are in the overworld.
10:10 A mob switch will affect all players on the server in that dimension, so it's important to be considerate in deciding where to build it, and when to use it. A mob switch will disable most mob farms in the dimension.
10:45 A chunk loading line from the spawn chunks can be used to automatically start the mob switch when the game or server restarts. Or you can use the /forceload command at the chunk loader.
12:29 Some other examples include mobs from spawners, vexes, endermites, mobs that teleport from other dimensions, mobs that exit boats or minecarts, lightning strikes that convert villagers and pigs into witches and zombified piglins, zombie reinforcements, zombification of villagers, duplication of shulkers, and summoning of withers and wardens.
13:33 The number of PILLAGERS in the trap can build up very rapidly, making this an attractive option for some larger servers.
14:25 This mob switch is unusual in that it does not require a player to be present when stocking the mob switch with VEXES. Be sure to nametag the evoker.
14:46 SHULKERS are a great option for either overworld or nether mob switches, especially if you already have a shulker farm.
15:14 WARDENS are also an excellent choice for either overworld or nether mob switches.
15:37 Use 2 observers looking at each other to repeatedly trigger the trapdoor instead.