Get a WordPress attachment ID by it's filename. Searches '_wp_attached_file' post_meta values looking for matching filenames. If multiple are found the most recent ID by post_date is returned.

get_attachment_id_by_filename.php

<?php
/**
 * Search post attachments where the given filename matchs the attached file path
 * 
 * @link https://wordpress.stackexchange.com/a/405142/2744
 *
 * @param  string $filename The filename to search
 *
 * @return int The attachment ID of the first result sorted by post_date in reverse chronological order (most recent first)
 */
function get_attachment_id_by_filename( $filename = '' ) {
	global $wpdb;
	$like          = '%' . $wpdb->esc_like( $filename );
	$attachment_id = $wpdb->get_var(
		$wpdb->prepare(
			"
			SELECT
				post_id
			FROM
				`$wpdb->postmeta`
				LEFT JOIN `$wpdb->posts` ON `$wpdb->postmeta`.post_id = `$wpdb->posts`.ID
			WHERE
				`$wpdb->postmeta`.meta_key = '_wp_attached_file'
				AND `$wpdb->postmeta`.meta_value LIKE '%s'
			ORDER BY
				`$wpdb->posts`.post_date DESC
			LIMIT 1;
		",
			$like
		)
	);
	return absint( $attachment_id );
}

var_dump( get_attachment_id_by_filename( 'my-file-name.png' ) ); // Returns an ID like 123 if found or 0 if nothing is found