Reading the docs, it was not clear to me how to get this work with ChartJS4 in my context of a web app (Vue or React).
Through trial-and-error, I discovered I simply needed to add:
import ChartDeferred from 'chartjs-plugin-deferred'
ChartJS.register(<my other registrations>, ChartDeferred)
Maybe I missed it or I'm overlooking something obvious, this doesn't seem to be mentioned anywhere in the main git readme or the npm page for this library.