For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fsirl:doxygen-libclang/openSUSE_Tumbleweed/home:fsirl:doxygen-libclang.repo
zypper refresh
zypper install doxygen
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fsirl:doxygen-libclang/15.6/home:fsirl:doxygen-libclang.repo
zypper refresh
zypper install doxygen
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fsirl:doxygen-libclang/15.5/home:fsirl:doxygen-libclang.repo
zypper refresh
zypper install doxygen
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fsirl:doxygen-libclang/15.4/home:fsirl:doxygen-libclang.repo
zypper refresh
zypper install doxygen