SyCo Entertainment was previously a joint venture with Simon and Sony Music Group (three divisions of SyCo, TV, Film and Music), and in July 2020 Simon bought out Sony's stake in SyCo Entertainment excluding SyCo Music.
As such existing artists, back catalogue and the SyCo Music brand all fold into the Sony Music Group as a wholly owned subsidiary. Since Simon has since left SyCo Music as well, it may be that Sony no longer want to use a brand that is more associated with Simon Cowell rather than Sony and as such that is why SyCo Music has ceased to be used by Sony. So Simon shouldn't own any rights to the One Direction brand, the legal trademarks are owned by 1D Media Limited, which from research I can't see any shareholders other than the 1D guys.