Look in the /etc/apache2/apache2.conf file for a line that reads
Require all denied
Make sure this command is being used for the directory where your site is located. If so, switch to
Require all granted
Caution: Do not make this edition for all directories, only for the directories where you know you want to give permission to access.
If this is the problem, it must have been caused by updating the Apache configuration files. Note that when updating Apache (or any other similar software) the updater asks if it should replace the configuration files. If this question is asked, it is worth analyzing what changes have occurred in the configuration file. Eventually it may be worth keeping the old configuration file. If you want to use the new file it is important to redo the settings that existed in the previous one.