When I tried to upgrade my 1.18.2 world to 1.19, despite everything being upgraded properly (I think so), the world crashed when it tried to load. I then tested it with a fresh 1.19 world with the same datapack (that is attached) - when the world loaded, custom dimension isn't on the list for "/execute in" command. On next loading it crashes. Crash report is also attached.

The reason this happens is because the dimension json directly inlines the dimension type, instead of defining it in a separate file and then referencing it.

java.lang.IllegalArgumentException: Dimension must be registered, got Direct{cxx[fixedTime=OptionalLong.empty, hasSkyLight=true, hasCeiling=false, ultraWarm=false, natural=true, coordinateScale=1.0, bedWorks=true, respawnAnchorWorks=true, minY=-64, height=384, logicalHeight=384, infiniburn=TagKey[minecraft:block / minecraft:infiniburn_overworld], effectsLocation=minecraft:overworld, ambientLight=0.0, monsterSettings=a[piglinSafe=true, hasRaids=false, monsterSpawnLightTest=[0-7], monsterSpawnBlockLightLimit=0]]}