[MM3-users] Problems after upgrading from bullseye to bookworm

I upgrade my server to bookworm. In the process python was upgraded from 3.7 to 3.9 . I reinstalled the virtualenv and the mailman packages. When I now start mailman-web, I get this in web/logs/uwsgi-error.log:

pkg_resources.DistributionNotFound: The 'flufl.lock>=4.0' distribution was not found and is required by hyperkitty

What did I miss?

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