Hermitcraft runs on Fabric - https://fabricmc.net/

Decked out requires a minimum simulation distance of 10 and render distance of 16.

Decked out uses the following mods
https://modrinth.com/mod/audioplayer/version/fabric-1.20.1-1.7.1
https://modrinth.com/mod/fabric-api/version/0.83.0+1.20
https://modrinth.com/plugin/simple-voice-chat/version/fabric-1.20.1-2.4.25

To play Decked Out with a working map, you need a second player with a map in their offhand at this location. These commands will teleport you and give you the correct map.
/tp @p -511.5 62.0 1737.5
/give @p minecraft:filled_map{map: 976}

You can use Open To LAN in the Game Menu to let another account join. The account with the map is best left in spectator mode.