For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Ximi1970:Toolchains:MinGW:latest:win64/openSUSE_Tumbleweed/home:Ximi1970:Toolchains:MinGW:latest:win64.repo
zypper refresh
zypper install mingw64-win_iconv
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Ximi1970:Toolchains:MinGW:latest:win64/15.4/home:Ximi1970:Toolchains:MinGW:latest:win64.repo
zypper refresh
zypper install mingw64-win_iconv