I'm using Balena Etcher to write the SD cards, as I know that it works well with the Raspberry Pi.
I started off the OS testing with retropie and didn't care for it at all. It's too stripped down, and too hard to get to things. Decided against it, as it seemed like quite a struggle. I'm not great with Linux though, so that's a big part of it.
Next I tried Alpine Linux, and couldn't figure out an easy way to install it. Steep learning curve is not what I'm looking for right now. Just need a quick proof of concept. Alpine is out for now.
I looked at Ubuntu Core IOT, but it requires an online account, and I'm sick of making accounts and being tracked by big corporations. Out.
Currently working on Ubuntu Server 20.04.1 for Raspberry Pi. So far, so good. It was easy to get an image and start flashing it to micro SD. Will see how big the installation size is, get a basic Libreto emulator core running on it, then strip out everything else I don't need. I also found another viable OS option: Linux From Scratch. The problem is that it will likely be a steep learning curve. It looks like a great starting point for something closer to a final OS solution.
I ended up having to run out and buy thrift store keyboard for this project. The lack of USB keyboard has beenb driving me nuts. Found a really nice Logitech for $3. Brought it home and cleaned it all up. Finally have Ubuntu Server 20.04.1 running on the Pi. Wifi is set up and running. Installing a GUI onto the server distro to make it easier to develop for. Only had to un a single command:
sudo apt-get install ubuntu-desktop.
That adds over 2GB to the image file size, but it's fine for testing. I imagine I can remove the GUI later, to test the simplified. I may need some of the gui code to display the game, but I can figure that out later.
The GUI is still installing, so it's more waiting around and reasearch.
It installed, but turns out that was just upgrading it to the entire Ubuntu Desktop, and now I have a bunch of crap like an office suite installed... Live and learn. I was pretty tired when I was doing all that. It's many hours later, and I've made homemade gingerbread cookies and snacked a bit. I'm done working on this for the night, so I'll end here.