Originally Posted by
m1234m
No one replied to this.

I wanted to reply to myself help others in this situation in the future.
I was not able to select my seats in advance until online check-in, which oddly was not at 24 hours in advance but rather about 47 hours pre-departure. I got the notification via email from Saudia. Choosing seats was really easy to do, though. However, I suspect that some people were able to select in much further in advance since there were only 6/24 business seats available to choose from for my latter leg.
You
should be able to select seats. But there is a major awkwardness to the process: Saudi verifies your identity by send an SMS or email with a passcode each time you access "sensitive" information. Except I've never received the information without setting things up with a phone call. All very clunky.