Index: src/wp-includes/kses.php
===================================================================
--- src/wp-includes/kses.php	(revision 48566)
+++ src/wp-includes/kses.php	(working copy)
@@ -230,6 +230,7 @@
 			'border'   => true,
 			'height'   => true,
 			'hspace'   => true,
+			'loading'  => true,
 			'longdesc' => true,
 			'vspace'   => true,
 			'src'      => true,
Index: tests/phpunit/tests/kses.php
===================================================================
--- tests/phpunit/tests/kses.php	(revision 48566)
+++ tests/phpunit/tests/kses.php	(working copy)
@@ -767,6 +767,11 @@
 			),
 			array(
 				'img',
+				'loading="lazy"',
+				'loading="lazy"',
+			),
+			array(
+				'img',
 				'onerror=alert(1)',
 				'',
 			),
@@ -1352,4 +1357,26 @@
 			),
 		);
 	}
+
+	/**
+	 * Test filtering a standard img tag.
+	 *
+	 * @ticket 50731
+	 */
+	function test_wp_kses_img_tag_standard_attributes() {
+		$html = array(
+			'<img',
+			'loading="lazy"',
+			'src="https://example.com/img.jpg"',
+			'width="1000"',
+			'height="1000"',
+			'alt=""',
+			'class="wp-image-1000"',
+			'/>',
+		);
+
+		$html = implode( ' ', $html );
+
+		$this->assertSame( $html, wp_kses_post( $html ) );
+	}
 }