Some success!
I managed to get one of my two buttons into the right mode. The problem is I have no idea what did the trick. I also haven’t been able to repeat it with my second button.
I was trying to do things like manually read attributes as is done for “tuya magic”, plus setting the operational mode. Then the switch became unresponsive again so I reset/repaired it. And then it worked!
On the subject of tuya magic: is this something that the current code/ddf does? eg I see talk of this at Including standard Tuya "magic spell" sequence during joining - #27 by cornim and indeed there is nothing like this in the DDF for my devices, but maybe the magic is implemented elsewhere?
Looking at other projects eg z2m I see that they have used the magic spell for these devices.