@tm1000 Thank you for the information!
Instead of patching bootstrap.php (which will trigger a security warning) I was able to remove PHP deprecation warnings from my logs by adding to /etc/freepbx.conf:
$bootstrap_settings['freepbx_error_handler'] = false;
require_once('/var/www/html/admin/libraries/utility.functions.php');
set_error_handler('freepbx_error_handler', E_ALL & ~E_DEPRECATED & ~E_STRICT);