For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h:X11:xfce:4.19/openSUSE_Tumbleweed/home:manfred-h:X11:xfce:4.19.repo
zypper refresh
zypper install xfwm4
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h:X11:xfce:4.19/openSUSE_Slowroll/home:manfred-h:X11:xfce:4.19.repo
zypper refresh
zypper install xfwm4
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h:X11:xfce:4.19/15.6/home:manfred-h:X11:xfce:4.19.repo
zypper refresh
zypper install xfwm4