Syndace [1] filed a deletion request for python-omemo-backend-signal [2]: This package is obsolete. Its purpose as a backend for python-omemo has been obsoleted by a rework of the python-omemo library and the upstream has been archived since 2022. All known previous applications using python-omemo-backend-signal have since been migrated to use the reworked python-omemo. Souce: I am the author.
[1] https://aur.archlinux.org/account/Syndace/ [2] https://aur.archlinux.org/pkgbase/python-omemo-backend-signal/
