I'm afraid I've been using Linux for so long that I'm not very knowledgeable about backup software for Windows. But I've been using Duplicati for a single Windows computer for years, and it's apparently also running on Linux. I never tried on Linux though, so don't take my words for cash.

There's also Duplicity, but it's command line and will probably require installing the Windows Subsystem for Linux. There's also Bacula but it's mostly for businesses. This Wikipedia page may know more than me.

On Linux, Deja Dup acts as a graphical interface for Duplicity, is easy, and is the default for GNOME and Cinnamon. Compatible with Duplicity but as mentioned, it's complicated for Windows.

However I think those are "too complicated" (I prefer raw files instead of archives) and for Linux I've been using rsync with a job scheduler (cron) for years. It's technically not a backup solution in itself but many backup software, like those mentioned, use rsync in some form anyway. Unfortunately it does not work on Windows. My strategy is to use rsync to copy my important files to an older HDD, then the very important files are also sent on an online drive.

The TLDR would be to give Duplicati a try if you really want a backup solution that is cross platform and graphical. Otherwise, there's nothing more certain than making copies yourself.

I guess I don't need to remind you to be careful. Take your time. Try restoring to be sure it works. Good luck!