Interface has been updated and there's a bunch of other updates too. They now provide their own syncing without relaying on third party software. Also, there is now a mobile app with which you can sync.

Link to source: https://github.com/BoostIO/BoostNote.next/releases

EDIT: Actually, now that I take a closer look at it, this is a new app developed by the same team. Does it still count as an update? Or should it be an addition?

Old version: https://github.com/BoostIO/Boostnote
New version: https://github.com/BoostIO/BoostNote.next

Apologies for the mistake.