Hello,
This is an issue on the A350 as well as the rest of the ini/MS default aircraft due to one simple thing: LODs. These aircraft utilize this new feature that is exclusive to FS2024. Other aircraft don't (yet, possibly never), that is why they don't have flickering shadows. If you go into the showcase (drone) camera, you'll see sharp shadows. This is a simulator limitation at the moment. We are in talks with Asobo on how we can resolve this simulator-wide. Hopefully we'll have a fix sooner rather than later.
Thank you for your understanding.