diff -pruN qtbase-everywhere-src-5.15.8.orig/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp qtbase-everywhere-src-5.15.8/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp
--- qtbase-everywhere-src-5.15.8.orig/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp	2023-03-24 14:40:24.844713011 +0900
+++ qtbase-everywhere-src-5.15.8/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp	2023-03-29 19:50:13.097003358 +0900
@@ -954,6 +954,7 @@ void QFontconfigDatabase::setupFontEngin
     QFontEngine::GlyphFormat format;
     // try and get the pattern
     FcPattern *pattern = FcPatternCreate();
+    FcPattern *match = NULL;
 
     FcValue value;
     value.type = FcTypeString;
@@ -980,7 +981,41 @@ void QFontconfigDatabase::setupFontEngin
     FcConfigSubstitute(nullptr, pattern, FcMatchPattern);
     FcDefaultSubstitute(pattern);
 
-    FcPattern *match = FcFontMatch(nullptr, pattern, &result);
+    if (!fid.filename.isEmpty()) {
+        // FC_INDEX is ignored during processing in FcFontMatch.
+        // So iterate FcPatterns directly and find it out.
+        FcFontSet *fcsets[2], *fcfs;
+
+        fcsets[0] = FcConfigGetFonts(nullptr, FcSetSystem);
+        fcsets[1] = FcConfigGetFonts(nullptr, FcSetApplication);
+        for (int nset = 0; nset < 2; nset++) {
+            fcfs = fcsets[nset];
+            for (int fnum = 0; fnum < fcfs->nfont; fnum++) {
+                FcPattern *fcpat = fcfs->fonts[fnum];
+                FcChar8 *fcfile;
+                FcBool variable;
+                int fcindex;
+
+                // FIXME: Ignore a FcPattern which has variable=true at this point.
+                if (FcPatternGetBool(fcpat, FC_VARIABLE, 0, &variable) == FcResultMatch &&
+                    variable == FcTrue)
+                    continue;
+                if (FcPatternGetString(fcpat, FC_FILE, 0, &fcfile) == FcResultMatch &&
+                    FcPatternGetInteger(fcpat, FC_INDEX, 0, &fcindex) == FcResultMatch) {
+                    QByteArray f = QByteArray::fromRawData((const char *)fcfile,
+                                                           strlen((const char *)fcfile));
+                    if (f == fid.filename && fcindex == fid.index) {
+                        // We found it.
+                        match = FcFontRenderPrepare(nullptr, pattern, fcpat);
+                        goto bail;
+                    }
+                }
+            }
+        }
+    }
+bail:
+    if (!match)
+        match = FcFontMatch(nullptr, pattern, &result);
     if (match) {
         engine->setDefaultHintStyle(defaultHintStyleFromMatch((QFont::HintingPreference)fontDef.hintingPreference, match, useXftConf));
 
@@ -1000,6 +1035,11 @@ void QFontconfigDatabase::setupFontEngin
                 antialias = fc_antialias;
         }
 
+        FcBool embolden;
+        engine->auto_embolden = true;
+        if (FcPatternGetBool(match, FC_EMBOLDEN, 0, &embolden) == FcResultMatch)
+            engine->embolden = embolden;
+
         if (antialias) {
             QFontEngine::SubpixelAntialiasingType subpixelType = QFontEngine::Subpixel_None;
             if (!(fontDef.styleStrategy & QFont::NoSubpixelAntialias))
diff -pruN qtbase-everywhere-src-5.15.8.orig/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp qtbase-everywhere-src-5.15.8/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
--- qtbase-everywhere-src-5.15.8.orig/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp	2022-11-11 16:29:17.000000000 +0900
+++ qtbase-everywhere-src-5.15.8/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp	2023-03-29 17:06:11.368989032 +0900
@@ -681,6 +681,7 @@ QFontEngineFT::QFontEngineFT(const QFont
     kerning_pairs_loaded = false;
     transform = false;
     embolden = false;
+    auto_embolden = false;
     obliquen = false;
     antialias = true;
     freetype = nullptr;
@@ -748,7 +749,7 @@ bool QFontEngineFT::init(FaceId faceId,
         FT_Set_Transform(face, &matrix, nullptr);
         freetype->matrix = matrix;
         // fake bold
-        if ((fontDef.weight >= QFont::Bold) && !(face->style_flags & FT_STYLE_FLAG_BOLD) && !FT_IS_FIXED_WIDTH(face) && !qEnvironmentVariableIsSet("QT_NO_SYNTHESIZED_BOLD")) {
+        if (!auto_embolden && (fontDef.weight >= QFont::Bold) && !(face->style_flags & FT_STYLE_FLAG_BOLD) && !FT_IS_FIXED_WIDTH(face) && !qEnvironmentVariableIsSet("QT_NO_SYNTHESIZED_BOLD")) {
             if (const TT_OS2 *os2 = reinterpret_cast<const TT_OS2 *>(FT_Get_Sfnt_Table(face, ft_sfnt_os2))) {
                 if (os2->usWeightClass < 700 && fontDef.pixelSize < 64)
                     embolden = true;
@@ -2102,6 +2103,7 @@ bool QFontEngineFT::initFromFontEngine(c
     antialias = fe->antialias;
     transform = fe->transform;
     embolden = fe->embolden;
+    auto_embolden = fe->auto_embolden;
     obliquen = fe->obliquen;
     subpixelType = fe->subpixelType;
     lcdFilterType = fe->lcdFilterType;
diff -pruN qtbase-everywhere-src-5.15.8.orig/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h qtbase-everywhere-src-5.15.8/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h
--- qtbase-everywhere-src-5.15.8.orig/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h	2022-11-11 16:29:17.000000000 +0900
+++ qtbase-everywhere-src-5.15.8/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h	2023-03-29 13:11:31.687717653 +0900
@@ -295,6 +295,7 @@ protected:
     bool cacheEnabled;
     bool forceAutoHint;
     bool stemDarkeningDriver;
+    bool auto_embolden;        // a flag to decide if embolden is set by fontconfig
 
 private:
     friend class QFontEngineFTRawFont;