I just found: Sound always go through hdmi
That symptom and workaround, which matches yours, would pretty much fit to the assumption that Picroft ships with a audio config that has not been updated yet to support the new RPi kernel audio interface changes.
… checking source code: https://github.com/MycroftAI/enclosure-picroft/blob/buster/etc/mycroft/mycroft.conf#L2
Okay pretty simple: The default Mycroft config forces audio output to card 0, which is HDMI only, if a monitor attached. These settings override the ALSA config.
Please edit /etc/mycroft/mycroft.conf and either change in the first two settings "hw:0,0" to "hw:1,0" or remove the card+device options completely so that the values are "aplay %1" and “mpg123 %1” and hence respect the ALSA settings (~/.asoundrc).
EDIT: Ah, since that config file will be overwritten on updates, AFAIK, better create/edit the local user override, which should be located at: $HOME/.mycroft/mycroft.conf
EDIT2: That should fix the issue so that raspi-config selection, respectively manual ALSA configuration is respected: https://github.com/MycroftAI/enclosure-picroft/pull/150
Btw, to review all sound devices and their card and device IDs, run: aplay -l