Hey guys,
I started building my Unity game at 84x48 resolution was struggling to get the actual build to look nice when resizing the window.
Luckily I found this guide by A. Durakin on how to fix this issue and wanted to share it with you:
https://itch.io/t/129513/unity-guide-upscaling-your-low-rez-game
When following it, use the correct Nokia resolution instead of 64x64 obviously.
Now my game looks nice and crisp at all window sizes (and in fullscreen mode).
Good luck everyone! :)