Linux

Yep that can work. But ignores all the well documented and supported development community comments I pointed to while also indicating other options exist.

As for.

Turning some switches on and off while monitoring input values doesn’t sound very computationally intensive.

You realise IO wise that describes your keyboard and mouse interaction on the most powerful gaming PCs.

It's what you do with the results that matters.

GPIO supports a fair bit more then the on and off input and output. It's slow compared to other systems. But has multiple serial protocols of differing types. Simple GUI displays can also be run via gpio connections. Low Res Lidar devices are available connected via the spi connections with all the data processed on that host PC.

So no gpio use can require all levels of processing power post connection. It is after all designed for experimentation and prototyping.

For my project. You clost to correct. I just use a simple GUI displays with xorg. So a pie 0 is plenty. And way lower power then the other options. It links to a pwm controller to power 2 12v 200w water tank heaters a relay for a 750w AC heater. Bluetooth connection to a BMS and solar MPPT. While operating multiple temp sensors measuring at different levels. And warning of legionaries risk. If the tank has not been over 65c in 14 days (actually 10 days but I'm over careful given the health status of my brother and I).

So much less then the tiny Pie 0 would not be able to cope but mainly due to the need for the vision impaired interface. Speaking functions dose not take much. But doing so without being unusably slow is about the limit of a pie 0.