Azure DevOps Server 2019: Custom Dashboard Widget not available - azure-devops

Question

We have a self-hosted Azure DevOps Server 2019 for which I have created my own widget using the tutorial https://learn.microsoft.com/en-us/azure/devops/extend/develop/add-dashboard-widget?view=azure-devops-2019.
I was also able to successfully add the extension to the server and the extension is also visible.
However, when I edit my dashboard, my newly created widget is not displayed. What could be the reason for this?
Furthermore, I also installed the extension VstsDashboardWidgetProjectTemplate (https://github.com/GregTrevellick/VstsDashboardWidgetProjectTemplate) in Visual Studio and also created an extension/widget from it. Unfortunately with the same result that I can install and see the extension, but not the actual widget.
I am attaching the vss-extension.json file as I suspect this is where the error is most likely to be found. However, I can also supply the other files if needed.
{
"manifestVersion": 1,
"id": "MyVeryFirstCustomExtension",
"version": "1.0.0",
"name": "My Very First Custom Extension",
"description": "Samples containing different widgets extending dashboards",
"publisher": "MyCompany",
"categories": [
"Azure Boards"
],
"targets": [
{
"id": "Microsoft.VisualStudio.Services"
}
],
"icons": {
"default": "img/logo.png"
},
"contributions": [
{
"id": "HelloWorldWidget",
"type": "ms.vss-dashboards-web.widget",
"targets": [
"ms.vss-dashboards-web.widget-catalog"
],
"properties": {
"name": "Hello World Widget",
"description": "My first widget",
"catalogIconUrl": "img/CatalogIcon.png",
"previewImageUrl": "img/preview.png",
"uri": "hello-world.html",
"supportedSizes": [
{
"rowSpan": 1,
"columnSpan": 2
}
],
"supportedScopes": [
"project_team"
]
}
}
],
"files": [
{
"path": "hello-world.html",
"addressable": true
},
{
"path": "sdk/scripts",
"addressable": true
},
{
"path": "img",
"addressable": true
}
],
"scopes": [
"vso.work"
]
}