When the text of a notification gets cut off, I keep wanting to make it wider so I can read more.
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!