Saudia seems to have become a serial wet lease airline taking planes where they can get it. Count yourself lucky the plane has a business class. I had a few times their 777s and most are ly-flat, some with 2-2-2 and some herringbone, and I had once an angled ly flat. For a JED-TUN leg I ended up on an A333 Wamos wetlease with angled ly-flat and no IFE (former Air Asia), which was slightly worse as their regular A330s. But there was no way to change since they only flew the wetlease to TUN. Maybe maybe SV will be ok with you to be rebooked on another time or day to a regular SV flight, but I cannot see them moving you to an alternative carrier for this - they will maintain you can still fly J. Contacting them is hit or miss.
https://www.saudia.com/experience/ab...ing-b777-368er
Help - Saudia downgraded flight TUN-JED