The way Edge Chromium handles downloaded .pdf files has bugged me ever since it was released and is still not working properly.
My System Viewer (default Windows application for .pdf files) is set to Foxit PhantomPDF as you can see here:
When I download a .pdf file in Edge you can also see the Foxit icon next to the file:
However, when I click "Open file" it opens as a new Tab in Edge and NOT in Foxit Phantom:
This happens regardless of how the option "Always open with system viewer" is set, i.e. both when it is OFF and ON:
In older versions (up to 89.0.774.75 (Official build) (64-bit)) it was possible to right click and then choose “Open with System Viewer” manually. Not ideal but a workaround nonetheless:
With the latest version the only option is to click on “Show in folder” and then open the default .pdf via Windows Explorer: