When WordPress says you are using an insecure version of PHP but you just upgraded it.

WordPress says you have to upgrade your insecure version of PHP 7.0.  PHP 7.4 is the current version.

You have to add the repository, then update.

Ubuntu:

sudo add-apt-repository ppa:ondrej/php

sudo apt-get update

Debian:

sudo apt install apt-transport-https lsb-release ca-certificates

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 -sc) main” > /etc/apt/sources.list.d/php.list’

sudo apt update

Change to the php version.

sudo update-alternatives –config php

Enable the correct version in apache.

sudo a2enmod php7.4

Disable the old version.

sudo a2dismod php7.0

Then restart apache2.

sudo systemctl restart apache2