Comment # 6 on bug 1186267 from Christian Boltz

Indeed, nobody told AppArmor (especially abstractions/php) about PHP 8, but
OTOH the /etc/apparmor.d/php-fpm profile covers /usr/sbin/php-fpm*

As a hotfix, you can create a file /etc/apparmor.d/abstractions/php.d/php8 with
the following content:

  /etc/php{,5,7,8}/**/ r,
  /etc/php{,5,7,8}/**.ini r,
  /usr/lib{64,}/php{,5,7,8}/*/*.so mr,
  /var/lib/php{,5,7,8}/session_mm_* rwlk,
  /var/lib/php{,5,7,8}/sess_* rwlk,
  /var/lib/php{,5,7,8}/sessions/* rwlk,
  /usr/share/php{,5,7,8}/ r,
  /usr/share/php{,5,7,8}/** mr,

and then run   rcapparmor reload

I submitted these additions upstream as
https://gitlab.com/apparmor/apparmor/-/merge_requests/755 and to the AppArmor
package (SR 894865).