Would be nice to document what this is supposed to return similarly to how getClassStringObjectType and getObjectTypeOrClassStringObjectType are documented.

I added Return class-string<Foo> for object type Foo. ; is it enough ?

from my experience enum-case can generate a separate class of bugs, therefore I think we should have a separate test for it

I don't understand which test you expect since the bug was about class with hasProperty and an enum-case cannot have a property.

but it could have a method

I might be wrong but since an enum is final method_exists calls will be either always true or always false on it and the HasMethodType won't be added.

I'm getting

enum MyEnum
{
	case CASE1;
	case CASE2;

	public function someMethod(): bool { return true; }
}

class HelloWorld
{
	public function withEnumCase(): void
	{
		$entity = MyEnum::CASE1;
		assertType('class-string<Bug4890PHP8\MyEnum>', get_class($entity));
		assert(method_exists($entity, 'someMethod'));
		assertType('class-string<Bug4890PHP8\MyEnum>', get_class($entity));
	}
}

Do you have a test in mind ?

what about

enum MyEnum
{
	case CASE1;
	case CASE2;

	public function someMethod(): bool { return true; }
}

class HelloWorld
{
	public function withEnumCase(UnitEnum $entity): void
	{
		assertType('class-string<UnitEnum>', get_class($entity));
		assert(method_exists($entity, 'someMethod'));
		assertType('class-string<UnitEnum&hasMethod<someMethod>>', get_class($entity));
	}
}

$h = new HelloWorld();
$h->withEnumCase(MyEnum::CASE1);

might also be worth testing with templates