Twitch
You can download the phone version of Twitch from APKMirror or APKPure and install that. I haven’t tried it myself, but other users have reported that it works. Just make sure that you download the phone version, not the version for Android TV. You might need to use APKMirror’s or APKPure’s own installer programs.
Steam
You didn’t specify what steam app you want, but you can find different ones on APKMirror and APKPure. Please try those, and let us know in the Working Apps thread if you find one that works.
Google Play Store
To install the official Google Play Store, you need to have GMS certification for the device. Google has not agreed to certify the PicoPix Max, which means that it is not possible to do. Please see this post: Smart YouTube purchased items not working
Official Youtube
The official Youtube app by Google needs GMS, exactly like the Play Store. However, S-Youtube which comes preinstalled on the PPM is capable of almost everything that the official Youtube app can do. Have you tried using it?