Use the devel/md4c port.

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -847,12 +847,6 @@ IF(ENABLE_XLSX)
      ENDIF()
 ENDIF()
 
-CPMAddPackage(NAME md4c
-              URL https://github.com/mity/md4c/archive/refs/tags/release-0.4.8.tar.gz
-              URL_HASH SHA256=4a457df853425b6bb6e3457aa1d1a13bccec587a04c38c622b1013a0da41439f
-              EXCLUDE_FROM_ALL yes
-              OPTIONS "BUILD_MD2HTML_EXECUTABLE OFF")
-
 ########### Set some global variables ###########
 IF(UNIX AND NOT WIN32)
      IF(APPLE)
