The docs refer to the php.ini used in the docker and the location appears incorrect compared to the actual docker.
/etc/php/7.3/php/ does not exist, it appears to be /7.3/cli or fpm?
Cheers
drwxr-xr-x 1 root root 26 Aug 16 11:41 cli/php.ini
drwxr-xr-x 1 root root 62 Aug 15 21:50 fpm/php.ini
drwxr-xr-x 1 root root 698 Aug 15 21:50 mods-available