People who use out of service devices miss the part that a smartphone do not need only a rom aka operating system but also drivers. The modem is a not flashable and if it do not receive updates anymore its potentially vulnerable for exploits. Those devices should NOT be used as an online devices! Installing GrapheneOS on such devices give the falls believe that they are secure but thats NOT the case! Don‘t put the blame on GrapheneOS - Its Goole police that do not support updates over a bigger period. Google promises to support their newest devices for 8 years, so think about spending some money for a new device and donate to GrapheneOS for their great work all of us benefit from.