I fully agree @Jakob18
No need to install DFE anymore. On the contrary, it causes more problems than it helps.
So if I were you, I would start all over again. So install the latest version of OFOX (you already have it anyway), format data, then install ROM and Gapps (and Magisk) and off you go.
Regarding Google Assistant. I think it's due to the core version you used. To be honest, I'm not a fan of this version either. I always use the full version. Why? Because you can easily adjust the config and thus the packages that you want to have installed and don't have to install any packages later.
If you want to try this:
- as I said, you download the full package
- extract the nikgapps.config (located in the folder afzc/nikgapps.config)
- important now: set use_zip_config to 1 --> use_zip_config=1
- now you can select the packages you want with "0" (do not install) or "1" (install).
- for the assistant it is important to leave GoogleSearch, Velvet and assistant on "1".
Now copy the nikgapps.config back into the .zip and overwrite the existing ones. Then you have a working Nikgapps with all the packages you want.
You can find more information here: