Assassin's Creed Unity won't launch on Linux via Steam Play due to bad DLC metadata

[Ienzo]

I tried installing Assassin's Creed Unity on Linux via SteamPlay. I got the following error message:

Failed to request product key from Steam, please try again in a few minutes

According to this thread <https://github.com/ValveSoftware/Proton/issues/190https://github.com/ValveSoftware/Proton/issues/190>, this bug is due to the file appinfo.vdf which miscategorizes Ubisoft DLCs as being Mac games and tries to fetch a Mac key. I already have a Windows key for AC Unity, so the advice in this other thread <https://www.reddit.com/r/linux_gaming/comments/olyezd/assassins_creed_unity_failed_to_request_product/> doesn't work. People in the first thread were able to get AC 2 to work by modifying appinfo.vdf.

Now I downloaded the Steam Metadata Editor which can read and modify appinfo.vdf, but it apparently can't modify DLC metadata, so it's kinda useless for my needs because the issue is that I need to recategorize the DLCs of AC Unity to be Windows and not Mac. I do not know how else to edit appinfo.vdf. If you know a way to edit DLCs on appinfo.vdf, let me know.

What I need from Steam is to please fix SteamPlay to correctly categorize the DLCs of AC Unity to be Windows on Linux so it can run via SteamPlay.

[my new friend]

SteamPlay subforum in the Linux discussions. https://steamcommunity.com/app/221410/discussions/8/