Yes, I finally installed it via Flatpak. What a fun adventure! First, I had to install Flatpak with apt. Then, I downloaded the Foliate .flatpakref. I installed it with `flatpack install com.github.johnfactotum.Foliate.flatpakref`, which worked the first time!

No, it didn't. Of course, Flatpak let me know that my user account didn't have the ability to configure the remote repositories the Foliate flatpakref specified. I could have searched for the right way to do it, but installing as root seemed to work, and it runs fine as a regular user, too!

But, of course, it doesn't. It doesn't have the ability to open files from most folders. I see by searching that you set sandbox permissions in an application manifest file, but I'm not sure I'm that attached to doing any more of this.