For anyone looking for that answer, it’s here in the form of a text file as given by the branding docs.
Icons were not mentioned there, so this is getting into more ambitious source-file-changes territory.
There is a chance one could edit the .exe, but I don’t think I’m going to encourage attempting that.
If finally resigned to rebuilding, you could test whether editing the file from other topic changes text:
This looks like it’s in the Duplicati.Library.AutoUpdater.exe resources. If changed, please test well…