Constructor proxy is protected if class is

compiler/src/dotty/tools/dotc/core/NamerOps.scala

@@ -149,9 +149,11 @@ object NamerOps:
    */
   def addConstructorApplies(scope: MutableScope, cls: ClassSymbol, modcls: ClassSymbol)(using Context): scope.type =
     def proxy(constr: Symbol): Symbol =
+      var flags = ApplyProxyFlags | (constr.flagsUNSAFE & AccessFlags)
+      if cls.is(Protected) then flags |= Protected
       newSymbol(
         modcls, nme.apply,
-        ApplyProxyFlags | (constr.flagsUNSAFE & AccessFlags),
+        flags,
         ApplyProxyCompleter(constr),
         cls.privateWithin,
         constr.coord)

tests/neg/i22560.scala

@@ -0,0 +1,22 @@
+
+class A:
+  protected class B
+
+// This fails to compile, as expected
+val x = A().B() // error
+
+object C:
+  protected val p = "protected"
+  protected def getString() = "Hello!"
+  protected class D:
+    def d = D() // ok
+
+// This fails to compile
+// val y = C.p
+
+// And this also fails to compile
+// val z = C.getString()
+
+// However, this compiles just fine.
+val alpha = C.D() // error
+val beta = new C.D() // error