I have a game that I'm developing in Unity. The game will be released for Android, so I'm working with the Google Play Console. The thing here is that I don't know how to block (Made not available) some devices with certain properties. For example, I need to made my game NOT available for tablets and for devices that don't have at least 1 GB of RAM. Does anyone know how can I do this?
You can use the Android Manifest device compatibility properties to specify required device features like minimum screen size/density, memory/graphics specs, network/touchscreen/accelerator capabilities, etc. Google Play uses those properties to determine whether to show/hide your app for any given device.
However you should consider whether these are hard-and-fast minimum technical requirements, or whether you may need to make your game more adaptable to different devices. The Android device ecosystem is very broad, with manufacturers offering lots of mix-and-match combinations of device specs. If you are too specific in your minimum requirements, you could very easily spec yourself into a very narrow slice of the market.
Android users also tend to expect that any app/game that they've heard of as being "Available on Android" is available for their device, unless they have a really old device. So from a PR/Marketing perspective, you can also incur some ill-will by artificially setting minimum specs that are higher than necessary.