Random sale ad in Calendar This morning when I opened by computer, I saw a notification for an event that I never created.



I have not linked my email address on macbook and I'm not even from US. So why is there an event with some random website in my calendar? I checked which apps have access to calendar, and it came up empty. So is it just some harmless ad pushed by Apple or something malicious?
Seeing the event is unnerving but, thankfully, it is unlikely to be a virus or current problem with your MacBook.
Instead it is possible this event came from an unwanted e-mail; Mail.app on macOS and on iOS has the ability to add events discovered in your e-mails.
You can disable this feature using the steps from How to disable suggested events in Calendar on iOS and Mac:

How to disable Mail event suggestions on OS X
Do the following on your Mac with OS X 10.11 El Capitan or later:

Launch Mail.
Choose Preferences from the Mail menu.
Click the General tab.
Select Never in the drop-down menu labeled “Add invitations to Calendar”.