In almost all microwaves, the control circuitry or mechanical switches only ever switch 2-3 power circuits: motor+fan(+bulb sometimes separately) and the heating (transformer+diode+capacitor+magnetron) high voltage circuit. It can therefore only switch the heat between 0 and max, usually in a slow (15-30s period) PWM cycle (that hopefully does not coincide with the tray rotation period). The inputs can be manual only, or sometimes there is also a scale, moisture sensor and microphone, along with thermal fuses for safety.

I think the pizza setting is just generic medium one with short 50% cycles to allow the heat to spread. The popcorn setting can be much more interesting:
https://www.youtube.com/watch?v=Limpr1L8Pss

A powerbank is another step in energy conversion and the cables are annoying.

Yeah, it’s fun but the temperature needs to be correct. With rising temperature, the paper goes black, light gray, brown and then glowing orange.

I am not aware of any receipt printers using lasers - thermal printers have an array of resistors that get hot when necessary. I know how a laser printer works and it is hard to explain in 12 or so words. Inkjets are way easier, you can just say “squirt squirt oops”. Anyway…

1. A photosensitive drum gets a negative electrostatic charge.
2. A laser shining through a rotating prism scans lines across the drum’s surface. This removes charge from parts of the drum that should not be covered in toner.
3. A high-voltage corona wire inside the toner reservoir charges an amount of toner positively.
4. The charged drum rotates past the corona wire, getting covered in toner where its negative charge remains.
5. Paper is pushed against the drum and the powdery toner is transferred to it.
6. The paper continues into a fuser, a little oven where a heating element briefly makes the toner so hot that it melts, its powder particles making a permanent bond among themselves and with the paper. (The heater is usually stationary and heats the paper from below. The fuser drum that pushes paper against the heater can get sticky and pick up some of the toner, making images repeat down the page. This is the most common failure mode that cannot be resolved through regular maintenance such as replacing the toner cartridge and printing cleaning pages. However, almost all laser printers have a cheap fuser module or its drum available so it is usually worth replacing.)

Time travel is a prerequisite but don’t worry, you can just

from __future__ import antigravity

Laser printers more accurately “bake paper so that number powder sticks to it”