i got curious about what rpg maker it is the game is built on and checked its folder. seem to be based on rpg maker 2003.

The original game was made in RPG Maker 2003, but the Enhanced Edition is made in Unity.

Not sure what folder you checked that made you think it's made in RPG Maker 2003. Half the files are called Unity.

it is still rpg maker. it uses version v2019.2.17.24627 which is newer than the steam version. it does have a number of plugins however. the plugins alters stuff like the interface and the stat point system. the game have 2 executables: one of which uses the default rpg maker 2003 menu system and one of which uses the plugins. both uses the same assets however(sprites and audio files).

I just installed it and it has the config in
    ~/.config/unity3d/Stegosoft\ Games/Ara\ Fell

Additionally the developers describe on their website:
* https://www.stegosoftgames.com/Press/index.php
"Ara Fell: Enhanced Edition
 For our kickstarter-funded game Rise of the Third Power, we wanted to break free of our RPG Maker trappings,
 to allow us to be able to implement the features we want and to make our game available
 on every gaming console we could, which in our eyes would elevate us from game dev hobbyists
 to game dev professionals. In order to make this happen, we created a new engine to run our game
 from scratch in Unity."

So it it should be Unity ...

I doubt this works like that but i am gonna ask anyway. Is it possible to buy the gog version and play it on android since my android tablet is better than my pc i think. Or should i buy it on google play if i want to play on android?
Bu then when i get a new pc i am gonna need to buy it again for pc on gog?

I am not in smartphones/tablets - as a Unix specialist this is not my world and both share Linux, the kernel, but Android is no GNU/Linux distribution ... so in that case Google Play may be the right place. Concerning getting a key/license when purchased on another platform is for me still confusing ... even considering GOG and Steam there may be a small time this is free ... or one has to ask ... but I tend to think that one would have to buy it twice in that case.
But as said I am not interested in these toys and never understood that people (can) use such small devices with bad screens and no reasonable input (from my point of view) and am myself longing for 8k - currently using 31.5" 4k ...
Hope this helps despite living in a different world. ;)