Scala 2 so far allowed patterns like this:

class Base {
 class Ops { ... }
}

class Sub extends Base {
 class Ops { ... }
}

Scala 3 rejects this with the error message:

6 | class Ops { }
 | ^
 |class Ops cannot have the same name as class Ops in class Base
 | -- class definitions cannot be overridden

The issue is that the two Ops classes look like one overrides the other, but classes in Scala 2 cannot be overridden. To keep things clean (and its internal operations consistent) the Scala 3 compiler forces you to rename the inner classes so that their names are different.

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