If custom dimensions are added via datapack, the optimize world feature would fail saying that the dimensions are unknown dimension types.

[17:57:26] [Render thread/INFO]: Loaded 2 recipes
[17:57:26] [Render thread/INFO]: Loaded 2400 advancements
[17:57:30] [pool-7-thread-1/ERROR]: Error upgrading world
java.lang.RuntimeException: Unknown dimension type : ResourceKey[minecraft:dimension / battle:dig_small]
at net.minecraft.class_3360.method_14745(class_3360.java:279) ~[client-intermediary.jar:?]
at net.minecraft.class_3977.method_43411(class_3977.java:77) ~[client-intermediary.jar:?]
at net.minecraft.class_3977.method_17907(class_3977.java:51) ~[client-intermediary.jar:?]
at net.minecraft.class_1257.method_5404(class_1257.java:132) ~[client-intermediary.jar:?]
at java.lang.Thread.run(Thread.java:833) [?:?]