Thanks for the tip @wakest! Firmware is 20251118.
I am suspecting that the keyboard issues is somewhat related to the lid position (some others also reported similar suspicions). When I don’t move the lid, the keyboard is usually OK, and sometimes by moving the lid I can make the unresponsive keyboard come back to life.
If by moving the lid back and forth temporarily fixes the issue, then it must be something to do with the cabling. Have you tried removing the top plate around the keyboard and tried to look if the two JST connectors on either side of the OLED move when you bend the hinge back and forth?
I checked the JST connectors, they look fine. It is happening somewhat less lately, but still happening. A mystery for me… 
Maybe something to do with the cables near the hinges…
As a data point, I have occasionally been able to temporarily resolve the issue by removing the top plate and pushing the cable on the right a bit deeper into the hinge.