TL;DR: it's not possible to export data from Arc, but it's possible to copy-paste the folder to a Chrome profile, and Firefox and other browsers will detect&import it.
Unfortunately, Zen Browser simply isn't an alternative. If you like Arc, then Zen's UI for tabs and splitting views isn't really anywhere close to satisfying the same needs.
I was literally using Arc because of the ability to hide most of the userchrome.
Every time I open split views or tabs I curse. I've said this in the past but layering view multiplexors has to be the most stupid modern "super-user" trap. You have the ability to open multiple browser windows and composite them side by side, use it.
Does anyone know of any other browsers that are chromium based and have very little features aside the ability to hide most of the UI?
Firefox seems to be borrowing some of the UI features slowly (at least the vertical tabs). And at least the Mozilla Foundation is very public with their wants and goals.
TL;DR: it's not possible to export data from Arc, but it's possible to copy-paste the folder to a Chrome profile, and Firefox and other browsers will detect&import it.