[pjc50]

I think this isn't due to the TUI itself (and this one isn't text, it has images in!) but downstream of a whole load of other choices. You rarely have this with game UIs, for example.

It's not just the use of immediate mode, but a whole stack of design decisions to prioritize snappiness.

[Vampiero]

Consider how quickly conhost.exe starts compared to the new cmd.exe

Most of it is because of ancillary stuff and heavy dependencies.