It’s not clear how much European debt Saudi Arabia holds, but its central bank’s net foreign currency reserves stand at $445bn. Saudi Arabia holds $135.9bn in US treasuries, placing it 17th among investors in the US bonds.
Best info on their holdings I could pull from fake news coverage. I am going to assume they hold less EU than US. So lets say 130billion.
European sovereign bond issuance continues above pre-pandemic levels: in 2021, European sovereign bond issuance, including issuance from EU Member States, the UK and the European Commission, accumulated EUR 3362.3 bn in proceeds,
Note that's with a 3.3T
I am not a bond trader so I am not sure how big of impact Saudi sell off would cause but for them to drive the price, they would be taking big losses on top of what is likely an underwater position.