diff --git a/src/corelib/global/qflags.h b/src/corelib/global/qflags.h
index ab46af2d8e7..c6cbaa1adb2 100644
--- a/src/corelib/global/qflags.h
+++ b/src/corelib/global/qflags.h
@@ -205,6 +205,33 @@ constexpr inline void operator+(Flags::enum_type f1, int f2) noexcept = delete;
 constexpr inline void operator-(int f1, Flags::enum_type f2) noexcept = delete; \
 constexpr inline void operator-(Flags::enum_type f1, int f2) noexcept = delete;
 
+// restore bit-wise enum-enum operators deprecated in C++20,
+// but used in a few places in the API
+#if __cplusplus > 201702L // assume compilers don't warn if in C++17 mode
+  // in C++20 mode, provide user-defined operators to override the deprecated operations:
+# define Q_DECLARE_MIXED_ENUM_OPERATOR(op, Ret, LHS, RHS) \
+    constexpr inline Ret operator op (LHS lhs, RHS rhs) noexcept \
+    { return static_cast<Ret>(qToUnderlying(lhs) op qToUnderlying(rhs)); } \
+    /* end */
+#else
+  // in C++17 mode, statically-assert that this compiler's result of the
+  // operation is the same that the C++20 version would produce:
+# define Q_DECLARE_MIXED_ENUM_OPERATOR(op, Ret, LHS, RHS) \
+    static_assert(std::is_same_v<decltype(std::declval<LHS>() op std::declval<RHS>()), Ret>);
+#endif
+
+#define Q_DECLARE_MIXED_ENUM_OPERATORS(Ret, Flags, Enum) \
+    Q_DECLARE_MIXED_ENUM_OPERATOR(|, Ret, Flags, Enum) \
+    Q_DECLARE_MIXED_ENUM_OPERATOR(&, Ret, Flags, Enum) \
+    Q_DECLARE_MIXED_ENUM_OPERATOR(^, Ret, Flags, Enum) \
+    /* end */
+
+#define Q_DECLARE_MIXED_ENUM_OPERATORS_SYMMETRIC(Ret, Flags, Enum) \
+    Q_DECLARE_MIXED_ENUM_OPERATORS(Ret, Flags, Enum) \
+    Q_DECLARE_MIXED_ENUM_OPERATORS(Ret, Enum, Flags) \
+    /* end */
+
+
 QT_END_NAMESPACE
 
 #endif // QFLAGS_H
diff --git a/src/corelib/global/qnamespace.h b/src/corelib/global/qnamespace.h
index 6bbe2426098..99678cf97e7 100644
--- a/src/corelib/global/qnamespace.h
+++ b/src/corelib/global/qnamespace.h
@@ -208,6 +208,7 @@ namespace Qt {
         // size of a multi-variant string.
         TextLongestVariant = 0x80000
     };
+    Q_DECLARE_MIXED_ENUM_OPERATORS_SYMMETRIC(int, AlignmentFlag, TextFlag)
 
     enum TextElideMode {
         ElideLeft,
@@ -215,6 +216,7 @@ namespace Qt {
         ElideMiddle,
         ElideNone
     };
+    Q_DECLARE_MIXED_ENUM_OPERATORS_SYMMETRIC(int, TextElideMode, TextFlag)
 
     enum WhiteSpaceMode {
         WhiteSpaceNormal,
diff --git a/src/corelib/text/qunicodetools.cpp b/src/corelib/text/qunicodetools.cpp
index be235aa0bf7..bf271223f73 100644
--- a/src/corelib/text/qunicodetools.cpp
+++ b/src/corelib/text/qunicodetools.cpp
@@ -1699,6 +1699,8 @@ enum MymrCharClassFlags {
     Mymr_CF_AFTER_KINZI = 0x00100000
 };
 
+Q_DECLARE_MIXED_ENUM_OPERATORS(int, MymrCharClassValues, MymrCharClassFlags)
+
 /* Characters that get refrered to by name */
 enum MymrChar
 {
@@ -1946,6 +1948,7 @@ enum KhmerCharClassFlags {
     CF_POS_MASK      = 0x000f0000
 };
 
+Q_DECLARE_MIXED_ENUM_OPERATORS(int, KhmerCharClassValues, KhmerCharClassFlags)
 
 /* Characters that get referred to by name */
 enum KhmerChar {
diff --git a/src/widgets/kernel/qsizepolicy.h b/src/widgets/kernel/qsizepolicy.h
index 5e948175f31..977f8008ead 100644
--- a/src/widgets/kernel/qsizepolicy.h
+++ b/src/widgets/kernel/qsizepolicy.h
@@ -199,6 +199,7 @@ private:
 Q_DECLARE_TYPEINFO(QSizePolicy, Q_PRIMITIVE_TYPE);
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QSizePolicy::ControlTypes)
+Q_DECLARE_MIXED_ENUM_OPERATORS(int, QSizePolicy::Policy, QSizePolicy::PolicyFlag)
 
 #ifndef QT_NO_DATASTREAM
 Q_WIDGETS_EXPORT QDataStream &operator<<(QDataStream &, const QSizePolicy &);
diff --git a/src/widgets/widgets/qframe.h b/src/widgets/widgets/qframe.h
index 144003bc0ef..2e97938c6b1 100644
--- a/src/widgets/widgets/qframe.h
+++ b/src/widgets/widgets/qframe.h
@@ -123,6 +123,8 @@ private:
     Q_DECLARE_PRIVATE(QFrame)
 };
 
+Q_DECLARE_MIXED_ENUM_OPERATORS_SYMMETRIC(int, QFrame::Shape, QFrame::Shadow)
+
 QT_END_NAMESPACE
 
 #endif // QFRAME_H
diff --git a/tests/auto/corelib/global/qflags/tst_qflags.cpp b/tests/auto/corelib/global/qflags/tst_qflags.cpp
index c252d797b21..e9caaf6dce4 100644
--- a/tests/auto/corelib/global/qflags/tst_qflags.cpp
+++ b/tests/auto/corelib/global/qflags/tst_qflags.cpp
@@ -35,6 +35,7 @@ class tst_QFlags: public QObject
 private slots:
     void boolCasts() const;
     void operators() const;
+    void mixingDifferentEnums() const;
     void testFlag() const;
     void testFlagZeroFlag() const;
     void testFlagMultiBits() const;
@@ -109,7 +110,41 @@ void tst_QFlags::operators() const
     CHECK(&, Qt::AlignHCenter, Qt::AlignHCenter, Qt::AlignHCenter);
     CHECK(^, Qt::AlignHCenter, Qt::AlignVCenter, Qt::AlignCenter);
     CHECK(^, Qt::AlignHCenter, Qt::AlignHCenter, Qt::Alignment());
+#undef CHECK
+}
 
+void tst_QFlags::mixingDifferentEnums() const
+{
+#define CHECK(op, LHS, RHS, RES) \
+    /* LHS must be QFlags'able */ \
+    do { \
+        QCOMPARE((LHS op RHS), (RES)); \
+        QCOMPARE((RHS op LHS), (RES)); \
+        /*QCOMPARE(( / *CTAD* / QFlags(LHS) op RHS), (RES));*/ \
+        /*QCOMPARE((QFlags(LHS) op ## = RHS), (RES));*/ \
+    } while (false)
+
+    // AlignmentFlags <-> TextFlags
+    {
+        CHECK(|, Qt::AlignCenter, Qt::TextSingleLine, 0x0184);
+        CHECK(&, Qt::AlignCenter, Qt::TextSingleLine, 0x0000);
+        CHECK(^, Qt::AlignCenter, Qt::TextSingleLine, 0x0184);
+    }
+    // QFlags<AlignmentFlags> <-> TextFlags
+    {
+#ifndef QT_TYPESAFE_FLAGS // QTBUG-101344
+        Qt::Alignment MyAlignCenter = Qt::AlignCenter; // convert enum to QFlags
+        CHECK(|, MyAlignCenter, Qt::TextSingleLine, 0x0184U); // yes, unsigned!
+        CHECK(&, MyAlignCenter, Qt::TextSingleLine, 0x0000U); // yes, unsigned!
+        CHECK(^, MyAlignCenter, Qt::TextSingleLine, 0x0184U); // yes, unsigned!
+#endif
+    }
+    // TextElideMode <-> TextFlags
+    {
+        CHECK(|, Qt::ElideNone, Qt::TextSingleLine, 0x0103);
+        CHECK(&, Qt::ElideNone, Qt::TextSingleLine, 0x0000);
+        CHECK(^, Qt::ElideNone, Qt::TextSingleLine, 0x0103);
+    }
 #undef CHECK
 }