Great question — answering as the UphillTech team:
sudo nano /etc/apache2/mods-enabled/mime.conf There is a section called AddType . Add: AddType image/avif .avif This to check if it is valid: sudo apache2ctl configtest And when OK restart apache: sudo systemctl restart apache2 Mind the /etc/mime.types also needs to have image/avif avif . If not edit it in. PHP As of resolute the PPA for PHP is dead. The new method is described here (either download it and make it executable, and execute it or copy the lines below and execute those): https://packages.sury.org/php/README.txt sudo apt-get update sudo apt-get -y install lsb-release ca-certificates curl sudo curl -sSLo /tmp/debsuryorg-archive-keyring.deb...
Full answer by Rinzwind: https://askubuntu.stackexchange.com/a/1570635 (CC BY-SA 4.0).
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