This is a low priority topic until all the functionality works as intended, since it only deals with the UI representation.
The navigation bar has been split into two. Classic timelines in the bottom, user configurable ones in the top.
This may lead to situations where the user may think they are in another timeline than they are actually in.
Especially if the user configures only one custom timeline, the UI will display this timeline name very prominently in quite large letters on the top of the screen, even if one of the timelines from the bottom is selected and it's name is displayed at the bottom in a small font.
This has managed to irritate me several times, until I learnt to look for all the littel clues the UI provides (custom timeline is underlined in blue when active; active classic timeline gets it's name displayed below the icon).
So I'd say this behaviour is surprising for new users - and surprise is never a good thing in a UI ;-)
I'm not sure what's the best way to improve this. I really like the way this behaves in the old Fedilab app: All timelines are in the same navigation bar, the user can configure, which ones are shown and in which order. The only drawback might be that you may have to scroll the navigation bar in case there are more timelines than space.
This also saves screen real estate in the vertical direction.
Maybe the advantages of both concepts can be combined?
Have everything in one navigation bar and let the user decide if it's on the top or bottom (should the instance icon move to the bottom as well if the navbar goes down? If not, this would waste a lot of space; if yes, it would break well-known UI experience...).
Let the user configure the order of all elements in the bar as well as their design (could we use icons for custom timelines? Maybe from some generic icon collection as well as our own graphics?).
Could we configure the amount of space between the items?
These are only suggestions and I am well aware that I am talking about a major rework that would mean a lot of work and it's definitely nothing you'd want to dig in before there is at least a proper release version of the app.
Thanks a lot for all the effort you are putting into this!