Realms world upload error: "Cannot invoke "ctt.c()" because "this.b" is null"

When attempting to click "upload new world" under "reset world" in Java Realms, I get this error message:

Unable to load worlds

Cannot invoke "ctt.c()" because "this.b" is null

Update 2023-12-6

New error:

Unable to load worlds

Cannot invoke "net.minecraft.class_1940.method_8583()" because "this.field_25022" is null