A lot of removed Free to Play games were activated recently.

Login to SteamDB with your Steam account and preferrably install the SteamDB browser extension. Then go to https://steamdb.info/app/17080/ and click "Launch" while the Steam client is running or go to https://steamdb.info/sub/21293/ and click "Add free license". While it shouldn't work for delisted games, in some cases it still does, depending on how the free packages have been set up.

In this case it doesn't work anymore, so my guess is, that people got news of the game being delisted today and activated it just in time before that. Or the free package hadn't been set up correctly and people abused that and the publisher now corrected their mistake. They definitely have changed the free package today from available to unavailable.

You can also activate EVERY available free package on Steam at once here although I would very much not encourage doing that! A lot of people have regretted doing that in hindsight.

And last but not least I believe you can also use ASF to do that but I don't know the details about that. And that will also only work on packages that either are still available or not set up correctly.

1. Game announces delisting
2. People add game to library
3. Game delists
4. steamtracker adds the game to their list of delisted games
5. steamtracker updates their database of people's owned games
6. All the people who added the game previously show up as "new activations"

I get added on steam by random people asking how I obtained a random game after delisting all the time. I always grabbed those games before delisting.