just to note, on github I obvously found examples for PicoMite/PicoCalc, so okay ... got the PicoCalc few months back and only 2 weeks ago mounted it to test also there the 7xtgv TUI prototype; with some 3d printed "kbd paper overlay carrier", his keyboard can be used to test also that "extended ITU-T" layout in design, both using as vertical/horizontal, allowing 5x5 or 6x5/5x6 matrix (kbd has own stm32 mcu, nice separation) - display is squared 4" 320x320 only over SPI; quite expensive; had in mind something tiny/cheap too;
this is not too much retro device, but useful for simulations (RunCPM and Fuzix too);
P.