beltonvip It's likely a USB connectivity issue, and possibly caused by the cable you are using is not of sufficient quality to flash an OS.
Many USB-C to USB-A cables will work fine, I suggest that you try using another cable.
If you continue to encounter issues, I suggest that you join the GrapheneOS chatroom on Matrix. The community will be able to help you troubleshoot your installation there: https://matrix.to/#/#grapheneos:grapheneos.org