Currently, the only way to see what is available offline is to go into the notebooks shortcut from the hamburger menu.
There, all notebooks currently being synchronized have a green progress bar.
Problem :
The progress is impossible to see. I have no idea how fast is the sync going or if it's even working
it doesn't stat how many of the total amount of notes from the notebook has already been synced
It looks awfully slow
Suggestion :
At the top of the screen, have a small dedicated space for sync progression
A number indicate the amount of notes that needs to be synced when you open the app
Another number indicated the amount of notes that have been synced
A progress bar for each note being synced (rather than for a whole notebook)
A very similar process works on the Spotify App which makes it easy to know how the offline player is doing under the hood