It looks to me that the connection of collectionView is broken between your ViewController.swift file and the outlet in your storyboard.
Did you happen to decide to make a spelling correction to the outlet name? If so then the method you should use to rename an IBOutlet or an IBAction is to right click on the name and then select Refactor > Rename. That method ensures that the names are changed correctly in both the Storyboard and the ViewController.
To fix it in this case place the project into “Assistant Editor” mode and recreate that connection. You will likely have a residual broken connection in storyboard so to fix that you need to right click on the View Controller in the document outline which will reveal a panel like the one below. If you see any connections with an Amber triangle to the right then click on the little x to the left of the name to remove it.