Steps to reproduce the issue

Login with Administrator account (not super administrator)
Edit startpage article
Click save & close

500 Error

KExceptionError | Fatal Error [500]
Error: Maximum execution time of 30 seconds exceeded
.../libraries/vendor/joomla/string/src/phputf8/mbstring/core.php:94

89 * @return mixed string or FALSE if failure
90 * @Package utf8
91 */
92 function utf8_substr($str, $offset, $length = FALSE){
93 if ( $length === FALSE ) {
94 return mb_substr($str, $offset);
95 } else {
96 return mb_substr($str, $offset, $length);
97 }
98 }
99

Error occurs both with frontend editing and backend regular article editing.

Super Admin Account works and has no error.
Administrator accounts can save other articles without error.

Expected result

Saving

Actual result

KExceptionError | Fatal Error [500]
Error: Maximum execution time of 30 seconds exceeded
.../libraries/vendor/joomla/string/src/phputf8/mbstring/core.php:94

89 * @return mixed string or FALSE if failure
90 * @Package utf8
91 */
92 function utf8_substr($str, $offset, $length = FALSE){
93 if ( $length === FALSE ) {
94 return mb_substr($str, $offset);
95 } else {
96 return mb_substr($str, $offset, $length);
97 }
98 }
99

System information (as much as possible)

Joomla: 4.3.4
PHP 7.4.30
MySQLi 10.1.48-MariaDB-0ubuntu0.18.04.1
Caching Disabled
Gzip Disabled

Additional comments