For moving probably the solution: 2 step motors (1 horizontally, 1 vertically)

I don’t know of any patent that is on basic printers. If PDF is patented: You could convert PDF and PS files on the computer and then send the raw pixel data to the printer.

Fingerprints: I think you mean the yellow dots. I guess they are totally voluntary by the industry. (If any expert reads this and know that’s wrong, please correct me.)

Again guessing: Ink doesn’t produce poisonous stuff, only laser and thermo printers do. Or?

Regarding re-use of existing cartridge design/system: would it be too hard to 3D-print a cartridge in our own format?

Also we need a very primitive CPU/processor/microcontroller and a very simple firmware. Just spray ink or not, then move the carriage horizontally, then vertically.

I am wondering about (a) the data cable and (b) the power source:

(a) could be serial, RS232 or USB.

(b) could be battery, USB, power adapter.

Windows -> GNU/Linux

KDE/Gnome -> JWM

TV -> Reading books

Twitter -> Fediverse

Coke/Cola -> Tea/infusion

Amazon -> Local bookshop

If the ecological costs would exist as financial costs for the companies, that would help a lot. Right now it is cheap to throw away poisonous waste, ship stuff from far away countries etc.

And I think you hit an important point when you said that the average consumer doesn’t reflect much.