Search for Steam on GFN, and play it like you normally do with a game
As you log in into Steam, follow these instructions to opt in Alpha 19 Experimental:
1) right click on 7 Days to Die in your library
2) select properties
3) click on the betas tab
4) click on the drop down menu
5) scroll down to reveal latest_experimental unstable build and click on it
Notes:
The game has some memory issues, so you need to expect crashes even when you open your inventory.
If you play on medium settings the game is less likely to crash. In addition, don't look at the tree's leaves.
Also, you need to do update to A19 Experimental manually every time you log in a game with GeForce Now. This is from what I know... I did some tests with Offline Mode, trying to stop the game from updating, but it didn't work