It would be great to add hosted vector tile layers into the Basemap widget in Web AppBuilder. Currently, hosted vector tile layers are not supported in the Basemap widget.
I'm not sure if I understand your question correctly but I am able to add my vector layer to the Basemap widget. You just have to import the vector layer to your portal, add the element with type "tile layer" to a new web map, save the web map and share it with a group inside your organization.
Only the thumbnails seem not to support vector tiles, but you can make a screenshot of a part of your map and overwrite the thumbnail.
Good luck and greetings from germany
This has been implemented, and vector tile layers will be able to be selected through the basemap widget in the Web AppBuilder The following article provides some additional information on this: How To: Add Esri vector basemaps to the default basemap gallery in Web AppBuilder for ArcGIS
Sorry for not getting back to you sooner, but I just saw your response. I tried out the basemap widget this morning and this functionality still does not work for me. I am working with custom vector tile basemaps produced from ArcGIS Pro, not Esri vector basemaps. See below:
Let me know if you have any thoughts or things to try. Thanks for the response.
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