No, the operating systems are not compatible - they have different CPUs and you can't run the same version on both. You can backup and restore your configs and roms from a system to another - see https://retropie.org.uk/docs/Updating-RetroPie/#backup-option-2 - if you wish to keep your ROMs/BIOS/configs/etc.

maybe a usb input

Ive been looking online for a capture device and they all seem to look cheap and plastic or from china for £10 lol. I might buy a cheap one an see if it works