Hey, we are using Qt only on the pure frontend GUI side. The rendering itself is using FreeType + HarfBuzz independantly of the GUI.
We chose this model explicitly to still be free to replace Qt with something else in the future - iff we have to.
The reason behind that decision is, that we actually started with GLFW3, and epically failed, because GLFW3's input model was inferior and the API that I needed was actually marked deprecated by the GLFW3 devs and they also stated that their input model is not good and needs a rework. That led me to the decision to look around and find something else.
I only wanted to keep the GUI framework dependency as minimal as possible.
We sadly do not have BiDi support just yet, I'd actually love to have that. So far I only know of 2 terminals capable of this: mlterm and gnome-terminal.
Unfortunatily I lag the skills of hacking this in except doing it naively. I'd be more than happy for external contributors knowledgable enough in the domain of BiDi, to help us out here. :)
Not that commenter, but I also use mlterm and have for years, even though I don't normally use BIDI or other ‘exotic’ language capabilities. It is just a terminal, in the do-one-thing-well sense. Its downside is its somewhat idiosyncratic configuration (although there is now a GUI for most of it, so newer users might not notice).