Warning: cannot verify server identity. Calendar.google..com

Hello, Mohammed-Abbas!

Thanks for reaching out to the Apple Support Communities! It sounds like you're seeing an error message about being unable to verify the server for a Google calendar. Do you subscribe to a calendar through Google? Let's take a look at Settings > Passwords & Accounts. Do you see a Gmail account in there? If so, and you don't use it, try deleting it. You can see the steps to remove the account in this article to Add an email account to your iPhone, iPad, or iPod touch under "How to set up your email account manually".

If you want to use these features, then there may be a password issue with your Google account. They may be requiring some kind of verification.

Let us know the results and have a great day!