The single platform is Steam. First you need to buy it and after you need to download it. If you see an third party app, DON'T USE IT. The most probaly is an virus or an malware. And if you don't catch a virus or a malware, is an older version or multiplayer will not work. I hope i helped you!
Now Secret Neighbor is available on Google Stadia. Googe Stadia is an in cloud gaming. https://stadia.google.com
You need to search only the official websites of the application developers.