Thanks for your replys.
Affinity Photo is supported by Timing, but not completely. Timing does recognize when Affinity Photo is used and also knows the filename, but it does not know in which folder this file is.
Here is a screenshot of Affinity Photo listed in Timing:
And this is how it looks for other Apps, for example Photoshop:
As you can see, for Photoshop is also the file path shown.
I already contacted the Timing developer, and he answered that Affinity Photo does not make the filepath accessible through the accessibility API.
I tried both Affinity Photo versions, from Mac App Store and directly from Serif.