What did you end up doing? I'm sure other people who find this topic will appreciate learning how you did it.
Viewing post in How to back up games (time sensitive)
I went through my "itch" files (windows key + r, %appdata% being the only way I know how to access them) and backed up the games and demos on to my external hard drive and zipping them. Not sure if it will work but to be honest most of my library is free to play stuff/demos so it isn't a big deal if I have to redownload them.