Answers for "install php 7.4 alongside php8"

install php7.4 in linux server

For install all important php 7.4 extensions
apt install php7.4-common php7.4-mysql php7.4-xml php7.4-xmlrpc php7.4-curl php7.4-gd php7.4-imagick php7.4-cli php7.4-dev php7.4-imap php7.4-mbstring php7.4-opcache php7.4-soap php7.4-zip php7.4-intl -y

install php 7.4

sudo apt install php7.4-common php7.4-cli php7.4-bcmath php7.4-bz2 php7.4-curl php7.4-gd php7.4-intl php7.4-json php7.4-mbstring php7.4-readline php7.4-xml php7.4-zip php7.4-fpm