Looks like qt5-static on mingw is completely broken, so do a dynamic build instead.

.github/workflows/ccpp.yml

@@ -72,7 +72,6 @@ jobs:
           mingw-w64-i686-zlib
           mingw-w64-i686-png2ico
           mingw-w64-i686-qt5-base
-          mingw-w64-i686-qt5-static
           vim
           zip
     - name: update-protobuf

.github/workflows/release.yml

@@ -36,7 +36,6 @@ jobs:
           mingw-w64-i686-zlib
           mingw-w64-i686-png2ico
           mingw-w64-i686-qt5-base
-          mingw-w64-i686-qt5-static
           vim
           zip
     - uses: actions/checkout@v3

Makefile

@@ -15,17 +15,17 @@ ifeq ($(OS), Windows_NT)
 	MINGWBIN = /mingw32/bin
 	CCPREFIX = $(MINGWBIN)/
 	PKG_CONFIG = $(MINGWBIN)/pkg-config
-	WX_CONFIG = /usr/bin/sh $(MINGWBIN)/wx-config --static=yes
+	WX_CONFIG = /usr/bin/sh $(MINGWBIN)/wx-config
 	PROTOC = $(MINGWBIN)/protoc
 	WINDRES = windres
-	LDFLAGS += \
-		-Lc:/mingw32/qt5-static/lib \
-		-static
 	CXXFLAGS += \
 		-fext-numeric-literals \
 		-Wno-deprecated-enum-float-conversion \
 		-Wno-deprecated-enum-enum-conversion
 
+	# For static qt5.
+	#export PKG_CONFIG_PATH = $(MINGWBIN)/../qt5-static/lib/pkgconfig
+
 	# Required to get the gcc run - time libraries on the path.
 	export PATH := $(PATH):$(MINGWBIN)
 endif

src/gui2/build.py

@@ -10,8 +10,8 @@ cxxprogram(
     srcs=[
         "./main.cc",
     ],
-    cflags=["$(WX_CFLAGS)", "-fPIC"],
-    ldflags=["$(WX_LDFLAGS)"],
+    cflags=["-fPIC"],
+    ldflags=["$(QT5_EXTRA_LIBS)"],
     deps=[
         "+fl2_proto_lib",
         "+protocol",