https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69880
--- Comment #13 from vsz.bugzilla at emailuser dot net --- Repeating the minimal tests with MSYS2 `mingw-w64-{i686,x86_64}-binutils-2.27-4-any` (the build that includes the proposed patch), it seems the problem is now fixed for both 32-bit and 64-bit targets. UPX 3.91 is silent now and the previously visible default manifest bits are no longer there inside the `.exe` files when a custom Windows resource is linked. Thanks to all for all the efforts and to Nick for the patch!