Into 2021.7: A new entity, trigger IDs and script debugging - Home Assistant explains:
“Our Docker images are now based on Alpine 3.13 and run Python 3.9… Please note, that Alpine 3.13 on ARM devices running a 32-bits operating system (armhf/armv7), requires your Docker version to be at least 19.03.9 (although, we recommend updating to an even higher version). Additionally, you need to have libseccomp 2.42 or newer.”
mystery solved!