Only RSS feed, iCal calendar feed is not available for issue due dates

My company’s using GitLab Community Edition. I found a related documentation page about due dates can be exported at iCal calendar feed in this link

So, I navigated to Assigned Issues page and click subscribe button, but it only returns to me an RSS feed with URL format (feed://

The question is can the iCal calendar feed can be turned on? How do I do it?