The mentioned package (and others) have the problem that mingwXX-libjpeg-devel could not be found. 

There have already been several attempts to fix problems found with the existing mingwxx-jpeg package (https://build.opensuse.org/request/show/1156265 and https://build.opensuse.org/request/show/1157028), with which the development package of jpeg is found by other packages in a linked project (https://build.opensuse.org/packageshow/home:rhabacker:branches:windows:mingw:win64/mingw64-jpeg). 

From https://build.opensuse.org/package/live_build_log/home:rhabacker:branches:windows:mingw:win64/mingw64-jpeg/openSUSE_Leap_15.4/x86_64: 
32 packages with a direct dependency to this package.
Packages: mingw64-abiword, mingw64-aqbanking, mingw64-breeze5-style:mingw64-breeze, mingw64-breeze5-style: mingw64-breeze4-style, mingw64-djvulibre, mingw64-gdk-pixbuf, mingw64-gegl, mingw64-gst-plugins-good, mingw64-imagemagick, mingw64-jasper, mingw64-kdelibs4, mingw64-khtml, mingw64-lcms, mingw64-lcms2, mingw64-libgxps, mingw64-libmng, mingw64-libqt4, mingw64-libqt4: mingw64-cross-libqt4-qmake, mingw64-libqt4: mingw64-libqt4-static, mingw64-libqt5-qtbase, mingw64-libqt5-qtimageformats, mingw64-libqt5-qtwebkit, mingw64-libwebp, mingw64-libwmf, mingw64-poppler, mingw64-tomahawk-unstable, mingw64-vigra, mingw64-webkitgtk, mingw64-webkitgtk3, mingw64-wv, mingw64-wxWidgets-3_0, mingw64-wxWidgets-3_2 

For unknown reasons, this does not work with this project. The build log (https://build.opensuse.org/package/live_build_log/windows:mingw:win64/mingw64-jpeg/openSUSE_Leap_15.5/x86_64) shows that no package depends on this.