Unless you make your host OS read-only, it itself will keep writing while running your docker containers. Furthermore slapping read-only in a docker container won’t make the OS you’re running in it able to run correctly with an RO root fs. The OS must be able to run with an RO root fs to begin with. Which is the same problem you need to solve for the host OS. So you see, it’s the same problem and docker doesn’t solve it. It’s certainly possible to make an Linux OS that runs on an RO root fs and that’s what you need to focus on.

I’m not sure why Docker would be a particularly good (or particularly bad) fit for the scenario you’re referring to.

If you’re suggesting that Docker could make it easy to transfer a system onto a new SD card if one fails, then yes that’s true … to a degree. You’d still need to have taken a backup of the system BEFORE the card failed, and if you’re making regular backups then to be honest it will make little difference if you’ve containerised the system or not, you’ll still need to restore it onto a new SD card / clean OS. That might be a simpler process with a Docker app but it very much depends on which app and how it’s been set up.