Multiple php versions are installed on ubuntu. You can find the config files of all the versions in /etc/php.
If you check the version on command line using
php --version
This version may be or may not be same as php version on browser (using apache2). You use phpinfo(); function to find the phpversion. You might have installed multiple php versions using apt-get install.
To shift different version on web using apache2
First disable the current enabled version using command
sudo a2dismod php7.0
then enable the other version which you want to use on web
sudo a2enmod php8.0
sudo service apache2 restart
To shift different version on terminal
sudo update-alternatives --set php /usr/bin/php8.0
