Sadly my old 2Tb My Cloud died - but WD did an RMA and replaced it (thanks for the support!).
The replacement runs the 2.x firmware instead of the 4.x one I had previously and I can see it has 512Mb of RAM and I’m fairly sure the old one had 256Mb. What else has changed - CPU different? It seems a little faster. Although that could be because I haven’t restored much.
Is it an arm cpu?
I also notice that the shutdown has vanished from the GUI. And indeed there is no shutdown in /sbin.
I’ve found a halt in /usr/sbin … also the last 4.x firmware seemed quite similar to debian. I’m not really sure what this is.