micwoj92 [1] filed a deletion request for libgfortran6 [2]: Package fails to build/download sources. This has been reported in 2019/2022 and is not fixed since. These files/libraries are already provided by `gcc6-libs` package which is maintained.
[1] https://aur.archlinux.org/account/micwoj92/ [2] https://aur.archlinux.org/pkgbase/libgfortran6/
