I love these kinds of simulation games in the style of mini motorways/ mini metro, and i had a lot of fun with it. I reached the stage where you have to occupy all nodes, but couldnt get ahead of that (there was only one node left in the grid so i didnt have anything to connect it with!). The upgrades system is well implemented and the minimalistic art also fit the limited shapes restriction and overall chill vibe of the game. My suggestion on improving this would be the UI - since most of the gameplay happens in the UI in these games, it would be really satisfying to have those little popping sounds every time you click an upgrade button or having the level ups shown in a more pleasing way. Also some points can be modified in the gameplay where you can remove some existing nodes.
But overall, nice work, this has really good potential!