You can download Recalbox 6.1 Beta 4 (pre-release) for GPi from https://archive.recalbox.com/
How to install a Micro SD Card image guide can be found at https://droidbox.co.uk/how-to/how-to-flash-a-retropie-sd-card-image-for-the-gpi/
How to install a Micro SD Card image guide can be found at https://droidbox.co.uk/how-to/how-to-flash-a-retropie-sd-card-image-for-the-gpi/