I always recommend adding a hard drive for the backups, verifying that the files are on it, verifying that a live distro or other computer can see them (might need different filesystem and copy again), unplug or remove the backup drive from the computer to be linux’d, then installing the distro.

I’ve installed some distros that combine all the drives by default. Literally the most cursed default possible, but then I have to use a different distro to split them because it wasn’t live and the installer can’t do it alone.