@nononoyes
I’ve realised that I have been approaching this from completely the wrong direction. Because I was using a USB stick and I use those for live-CDs I just assumed that I would have to make a live-CD and then make it persistent. WRONG!
All I had to do was get a USB stick that was big enough to install the operating system on That’s a normal operating system and is obviously persistent. I can install applications and save data. Easy.
It was 20GB, but that’s fine, it’s enough to install one extra application and to save a few small data files.
There may be a slight delay as it reads from the USB, but once the app is loaded into ram then it would be no different than if installed on an HDD or SSD. In most cases, if using a USB3 device the differences would be insignificant for most usage.
Most USB sticks aren’t designed for the data access patterns of an OS, so you may find that the USB stick doesn’t last very long. M.2 SSD’s get quite warm and usually have some passive cooling.
Small (128GB) M.2 SSD drives are not expensive (and there are many used M.2 SSD drives that were replaced with higher capacity models), and external USB3 cases. The external cases are designed to provide passive cooling, but are much large than a USB stick and require a cable. I have a couple of these (one PCIe NVME and one SATA) for testing or to run Fedora on MacOS or Windows boxes.
I’m only going to show a friend the app and then some images, so I’m not that bothered about this. I already have a small external drive that just plugs in with a USB plug, no power cable needed, but even that is a bit clumsy so I preferred to try a USB stick for my limited application.
Anyone who wants to use the OS intensively might want to take notice of what you say though.