Steps to reproduce the issue

<field
			id="created"
			name="created"
			type="calendar"
			required="false"
			label="JGLOBAL_CREATED_DATE"
			description="JGLOBAL_CREATED_DATE_DESC"
			class="inputbox"
			size="16"
			format="%Y-%m-%d %H:%M:%S"
            />

Expected result

Output of the Calendar field

Actual result

Output of the Calendar field
At the same time, a warning is issued.
Deprecated: Function strftime() is deprecated in ****/public_html/libraries/src/Form/Field/CalendarField.php on line 323

System information (as much as possible)

Additional comments