I have used readpst in the past to convert to mbox format - apt install pst-utils in a Debian qube. readpst -r FILE.PST will then create folders as defined in the pst
file, with the messages in each folder stored in mbox format. You can
then open them in mutt, Thunderbird, or another email client.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.