You need a device that tells you which fields to make black. And you'll need another device to verify the QR-code actually works.
You can use open source SeedSigner, that is ONE device not two, but I was just giving example of how this can be done.
Similar thing can be done in software level on any offline computer.
not by some machine you need to trust that ink will survive long enough without fading.
I trust my toner will last for centuries, and I don't think a black pen/marker can improve that.
Not a chance toner can last centuries.
They all have expiration dates, and printed ink is guaranteed to fade much faster than that, especially if you filled toner yourself or you kept it in bad air conditions.
Printer is also machine right? And your computer is also a machine, so you need two machines to print your paper wallet, that could leave memory history of you doing that, both in computer and in memory of printer.