I've found some e-readers that support Linux and Android such as FBReader, but are there any that can sync progress across the two?
There's a way, but it's kinda tricky.
There's a bunch of android apps which sync the progress across the devices (like Moon+ Reader). So, if you can set up an Android emulator on your Linux machine, that should do the trick.
FBReader supports this feature. They call it "book network".
It synchronizes reading progress and ebook files via Google Drive.
- On the Android device, go to Settings -> Synchronization and enable it.
- On Linux, install fresh FBReader (version 2.0.3 from
sudo snap install fbreaderworked for me but not the old one from the apt repo). Press the cloud icon, and everything seems to work afterwards.
Official tutorials: https://books.fbreader.org/tutorials.html.
FBReader is also available for iOS, MacOS, and Windows. While it was previously open source, now the snap packages a proprietary new version.