For openSUSE Backports SLE-15-SP5 Update run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:pgajdos:maintenance:php-APCu/openSUSE_Backports_SLE-15-SP5_Update/home:pgajdos:maintenance:php-APCu.repo
zypper refresh
zypper install php8-APCu
For openSUSE Backports SLE-15-SP4 Update run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:pgajdos:maintenance:php-APCu/openSUSE_Backports_SLE-15-SP4_Update/home:pgajdos:maintenance:php-APCu.repo
zypper refresh
zypper install php8-APCu