itch.io

If you have Steam installed (+Proton), you can

1. Download and unzip Descending
2. Click on "Games" in the toolbar (at the top of the client)
3. Click "Add a non-steam game to my library"
4. Browse for and select "Descending.exe"
5. Navigate to the game in your library
6. Select "Properties", then "Compatibility"
7. Check "Force the use of a specific Steam Play compatibility tool"
8. Select a Proton version (I used "Proton 9.0-4")
9. Launch the game from steam!

You can do this for most games that doesn't have a linux port.