How to protect reTerminal at power loss?

I will use the reTerminal in a situation where power will be cut abruptly. I need to protect the filesystem from becoming corrupted. Ideally the filesystem could be read only and reset to the same state at each reboot.

The reTerminal is currently running Ubuntu Server 21.10 arm64 + the reTerminal software to get the LCD etc to work. As I understand it this is a now a modified kernel.

$ uname -a
Linux rebuntu 5.10.92-v8+ #1514 SMP PREEMPT Mon Jan 17 17:39:38 GMT 2022 aarch64 aarch64 aarch64 GNU/Linux

I am trying to use overlayroot.conf to make the root file system read only, which is apparenly a standard feature in Linux/Ubuntu.

$ cat /etc/overlayroot.conf

This has no effect. The system works like normal. I also find now logs or errors about overlayfs/overlayroot.

How can I setup the reTerminal to be a robust embedded system that can tolerate sudden power loss and always boot up as if nothing happened?