The question you should be asking yourself is why aren't you using msys2? It has the best Linux compatible base and includes a lot more libraries than other mingw distributors. Perhaps they see msys2 as a superior release.
This is no longer a bug. Where are you installing mingw from? Use msys2.
I'm also having this issue. A solution for now would be to use msys2, install the MinGW version available (v7). And then prepend 'Experimental' into the filesystem header and namespace. Use the std flag, as you have. Link with '-lstdc++fs'. It does have a bug when removing files, no matter what one does - It will fail to delete due to permissions. But everything else seems to work.
I'm also having this issue. A solution for now would be to use msys2, install the MinGW version available (v7). And then prepend 'Experimental' into the filesystem header and namespace. Use the std flag, as you have. Link with '-lstdc++fs'.