I just duplicated widget acrcgis-map as is into my custom-widgets folder,
and then "npm start" failed.
I solved the problem when In line 18 of both files
arcgis-map/src/message-actions/filter-actions-settings.tsx
and
arcgis-map/src/message-actions/flash-actions-settings.tsx
I replaced
import ChooseConnectionType
by
import type ChooseConnectionType
ESRI - please check and tell whether I am right or not.