Can the macOS Notification Center be made wider?
I don't think this is possible on macOS. I looked for how developers deal with notification lengths and I found this: https://stackoverflow.com/questions/6307748/what-is-the-maximum-length-of-a-push-notification-alert-text

The discussion mostly seems to imply that developers don't have any control over how the notifications are displayed, but rather just standards they have to conform to. Hope that helps!