I think the easiest way to do this would be to remove the default copyright: https://docs.generatepress.com/article/changing-the-copyright-message/#removing-the-entire-footer-bar
Then add your copyright as a header widget in “Appearance > Widgets”.
Alternatively, you could hide the footer copyright on desktop:
@media (min-width: 769px) {
.site-info {
display: none;
}
}
Then hide the copyright widget you added to the Header Widget area on mobile. I would need to see it added in order to give you the correct CSS.
Let me know if you need more info ๐