If you mean the Unicode glyphs listed at https://en.m.wikipedia.org/wiki/Block_Elements they are supported - you just need a display driver that can render them. For example, `twin --hw=xft` (it's the default) or `twin --hw=X11`, both with a font that contains them

Given that it's drawing TUI windows, the MouseText characters for doing that very thing on the Apple IIe would seem even more pertinent.

* https://tty0.social/@JdeBP/114409020672330885