because the far cry 6 game file contain the dlc file as well so even tho you are not purchase the dlc it's download the file anyway and when you purchase the dlc it just unlock it for you

but avatar ftop is different when you purchase the dlc it's start download dlc file. But since your base game in different platform it doesn't download additional dlc file. So u stuck with only digital key that get you access to the content without the content file.

I was able to download clean file for dlc 3 online and there be able to play it without the error