Install php7.4 on Debian based machines. But first need to add ondrej/php ppa or source list file.

install-php74.sh

#!/usr/env sh
# To add this repository please do:

if [ "$(whoami)" != "root" ]; then
    SUDO=sudo
fi

${SUDO} apt-get -y install apt-transport-https lsb-release ca-certificates curl \
&& ${SUDO} wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg \
&& ${SUDO} sh -c "echo \"deb https://packages.sury.org/php/$(lsb_release -si | awk '{print tolower($0)}' ) $(lsb_release -sc) main\" > /etc/apt/sources.list.d/php.list" \
&& ${SUDO} apt-get update -y \
|| echo "Installing php7.4.x" \
&& ${SUDO} apt-get install -y \
php7.4-common php7.4-fpm php7.4-cli php7.4-dev php-ssh2 php7.4-zip php7.4-xml php7.4-json \
php-igbinary php7.4-ldap php-uuid php7.4-mbstring php7.4-intl php7.4-soap \
php7.4-curl php7.4-gd php7.4-xsl php7.4-bcmath php7.4-mysql \
php7.4-opcache php7.4-sqlite3 php-redis php-geoip php-ast php-xdebug \
&& echo "php7.4.x installed successfully"