@Mr.Blinky how to upload games to homemade arduboy?
You can use Arduino to upload games to your home made Arduboy. If you have built it with one of the features that require the homemade board package like the SH1103 display I2C display or something like that it will require you to compile the code with the board package selected and the correct settings.
The board package for this and instructions on how to use it are here: GitHub - MrBlinky/Arduboy-homemade-package: Arduino IDE board package for Arduboy and homemade versions making things easy
You can also use other uploading tools but in general it works just like any normal Arduboy, and by extension any normal Arduino Leonardo.