Index: src/wp-includes/kses.php
===================================================================
--- src/wp-includes/kses.php	(revision 54643)
+++ src/wp-includes/kses.php	(working copy)
@@ -2371,6 +2371,7 @@
 			'direction',
 			'float',
 			'list-style-type',
+			'object-fit',
 			'object-position',
 			'overflow',
 			'vertical-align',
Index: tests/phpunit/tests/kses.php
===================================================================
--- tests/phpunit/tests/kses.php	(revision 54667)
+++ tests/phpunit/tests/kses.php	(working copy)
@@ -1112,6 +1112,11 @@
 				'css'      => 'object-position: right top',
 				'expected' => 'object-position: right top',
 			),
+			// `object-fit` introduced in 6.1.
+			array(
+				'css'      => 'object-fit: cover',
+				'expected' => 'object-fit: cover',
+			),
 			// Expressions are not allowed.
 			array(
 				'css'      => 'height: expression( body.scrollTop + 50 + "px" )',