Install opl (debian)

sudo wget -O - http://rpms.litespeedtech.com/debian/enable_lst_debian_repo.sh | sudo bash
apt install openlitespeed

Install php

apt install lsphp81 lsphp81-{common,curl,mysql,opcache,imap,opcache,intl,imagick}
apt install lsphp82 lsphp82-{common,curl,mysql,opcache,imap,opcache,intl,imagick}
apt install lsphp83 lsphp83-{common,curl,mysql,opcache,imap,opcache,intl,imagick}
ln -s /usr/local/lsws/lsphp81/bin/php81 /usr/bin/php