Welcome to the forum, @artist
The following might help to understand PhotoLab…but will preserve a certain level of frustration regarding ARQ processing. 
Indeed. DPL imposes a few restrictions…
- https://support.dxo.com/hc/en-us/sections/5860036247197-Supported-Cameras-Lenses-Formats
- https://support.dxo.com/hc/en-us/articles/6940709955229-Are-additional-RAW-formats-such-as-sRAW-mRAW-RAW-S-HE-and-HE-etc-always-supported-if-a-camera-s-standard-RAW-images-are-compatible-
…and Sony ARQ file support has already been requested. Not many have voted for the feature though.
Find out about linear DNGs here:
As the page notes:
Typically, DNG files store unprocessed RAW data.
By contrast, Linear DNG files store some intermediate results of RAW conversion.
Some initial processing steps have been applied — but only linear ones.
This means that none of the data is lost to one-way, non-linear processes.
As a result, Linear DNGs have exactly the same flexibility as RAW files when it comes to editing aspects such as brightness, color, and contrast.
The last sentence mentions the flexibility “when it comes to editing aspects such as brightness, color, and contrast.” Alas, PhotoLab’s key features are not available.