Mac DLC with Windows game/DLC on Steam?

[NobleSpaniard]

My understanding is that if I own a game on Win/Mac, and change OS's, I can download and play (in the new OS) any supported games I own from the previous OS. If I'm wrong, please correct me. Otherwise:


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MY QUESTION:
Can you mix and match OS's when adding content (via Steam keys) within a given game, when it comes to games and DLC, as long as the DLC is supported on both platforms?

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Specifically, if I am given (or buy) the Steam key for the Mac version of an expansion/DLC (Gathering Storm for Civ VI, specifically) from a site like Fanatical... can I redeem the key for the Mac DLC on Steam, and play it on my PC, with the base game and other DLC in my account all being "for Windows" content?

I don't want to claim/activate the game key, if the content is not going to work seamlessly with the rest of the game. It was purchased for 19.99, without realizing it is tagged as "Mac OS," largely because it was half the price as the exact same content (39.99) for the PC on the Steam store (and elsewhere, for that matter). So, I'd certainly like to redeem the key and save twenty bucks (and hassle of trying to have him return the key), if it will work without wasting the twenty bucks already spent.

If it won't work... would someone who switched from Windows to Mac need to keep buying DLC tagged to "Windows," in order to successfully add the DLC to their Steam account, so that they could keep playing the game & DLC on their Mac?

Thanks in advance!

[_I_]

if the game and dlc are mac + windows, both will work

[NobleSpaniard]

Thank you very much.

Verified. I just bought the "Mac" version of Gathering Storm for half the price of the "Windows" version, and activated the key; and it added the game to my Civ 6 library (with no OS tags), and installed it for use.