Saudi Arabia sees a future, not too far off, where there is a sudden drop in demand for oil. Caused by electric cars.
In the US, 51% of oil becomes gasoline. https://www.quora.com/How-much-of-the-oil-production-is-cons...
A DCF model that does not take into account the rise of electric vehicles misses a very important point.
The IPO puts money in their pockets NOW based on future predicted profits. That money can be invested into true future technologies: EVs, clean energy, etc.
Why the IPO now? The rise of Tesla and BYD maybe? It's still a time when those are mostly unproven and so there are still plenty of skeptics and climate denialists who will buy up Aramco shares.