Any tips on riding a roll-off, followed by a trench? Any tips on riding this section of the trail? The land is sandy and the clearance afterwords is several meters.

I can't ride it slowly, as it is too steep and the sand will slide off. I suspect the suspension could probably handle the trench, but didn't try, let alone for jumping.

What is the correct way to pass this obstacle on a long-travel full-suspension bike? What about a rigid XC bike?
When I come across something like that, instead of riding straight down the hill I will head down across the hill on a diagonal. You can carry more speed this way and you won't hit the far wall of the trench and risk being sent over the bars, when your bike comes to an immediate stop.

This goes for any type of bike, rigid or full suspension.

If the risk of crashing in the ditch is low, I'll go straight down the hill while managing my speed. When at the bottom, simply lift the front end enough to clear the far side of the trench. This of course requires quite a bit of effort and/or skill depending on the surface of the ground, the slope you are descending the size of the trench.

Alternatively, get enough speed and jump the entire thing.