Thanks to my own tendency to hoard hardware, and a little help from some friends, I have confirmed that the Amadeus: A Riddle for Thee demo runs smoothly on:
A Win7 Dell laptop from 2011 with 4GB RAM
Win10 Desktop PC with dedicated GPU that was a really solid build in 2016 and is still quite serviceable for most needs
MacOS Mojave on a MacBook Pro Intel 2015
MacOS Big Sur on a MacBook Air M1 2020
every other MacOS/Windows computer people have tested on so far
I'm currently working on a Linux build to have another friend test that, but from that Win7 laptop alone I think it's pretty safe to say that this should run on just about anything. The application window is fully resizeable for any screen size, and the game will always render the 4:3 gameplay correctly with black bars on the side as needed. It can also be expanded to fullscreen.
I'm very excited about this. I love the thought of people playing this game on the same old computers that have been used to play the early-mid 2000s VN's that inspired it!