What you could do is edit the anomaly detection settings of the key user action to have only 101% traffic spike.
If the baseline is 0 traffic for that page, then if the traffic rises to 1 then you will get a problem appear in Dynatrace.
Then, create a tag for that application.
Next, you can create an application health tile for that single application on your dashboard.
Navigate to Applications in the left nav bar --> filter to your application by your tag --> rename the filter to the name of your app --> and click add to dashboard.
Your tile will appear like this:
And your users will be able to find out the reason your application is red by clicking into it and finding out.
@Geert U. This is actually quite simple. I would recommend marking the desired requests as key requests first. Once they are marked you can create custom graphs for them. You could also go up one level to the service that serves up that key request and tag it when a unique tag. From there you would just create a services tile and add a filter that looks at the newly created tag.
Let me know if you need any other assistance