No graphics at all, I want to run this machine headless and manage it using SSH. Applications will be web based. I tried running apt, apt-get or aptitude with -f and -m but that didn’t work.
When I search with apt-cache search for the missing dependency I get results that point to Ayatana, but when I install those, the dependencies are not satisfied.
But, I went for a different solution. I plan to run Debian only as host OS and run as much as possible via Docker containers. I was used to having Duplicati installed on Ubuntu on my current (old) NAS. This does have a lightweight desktop manager installed but I only use that on very rare occasions with Xvnc. So with this new Debian based NAS, I tried a dockerized Duplicati and that works for me. It is possible to map the / of the host OS to the Duplicati container as the source.
So, actually my original question isn’t answered, I have found a working solution since I already planned to use as much Docker containers as possible. Even backup does so now 
That’s the reason I’ll mark this as the solution.