/usr/share/dbus-1/services/org.fcitx.Fcitx.service is in fcitx-bin 1:4.2.9.1-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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[D-BUS Service] Name=org.fcitx.Fcitx Exec=/usr/bin/fcitx