I read on my samsung s6 tablet, my kindle paperwhite and occasionally my ubuntu laptop.

I use syncthing to keep the document folder completely in sync.

I've noticed when I open a new book on one device, and then decide I want to read it on another, I have to re-open it on each device to get it to show up in history. I prefer using History view to quickly jump between books.

Is there anyway to set up syncthing to sync the history/koreader settings between devices? Which files/folders would I want to sync? And is this a bad idea for some reason?

Ideally I could decide I want to open book X on device Y and have book X populated across all history views on all devices.
IIRC, the history stores absolute references to the filepaths, so, no, not without some "help".