I downloaded the trial to check my requirement, but it doesn't work:
I want to use the touchbar for an app that doesnt support touchbar directly.
Normally the touchbar show's only F1 ... F12 for this app, but I want to have functions
and/or icons visible on the touch bar when iI start the app.
- first I added the app to the touchbar
- then I added a trigger with button title "gear" and trigger action F7
then I started the app and expected to see "F1 ... F6 gear F8 ... F12", but still have F1 ... F12
It seems like you have not enabled the Touch Bar here to override the system one and what you are seeing is the same system one only. You can verify this by opening BTT and it should warn you at the top that "Your custom Touch Bar is currently hidden" clicking on that will bring up the button you created.
Is the eso app active? Possibly first try to add the trigger to the "All Apps" section, to verify it is working.
Also one thing that's important, System Preferences => Keyboard => Touch Bar shows must be set to "App Controls"