Can a brain aneurysm lower your iq?

No: If an aneurysm ruptures and damages brain, then damage can occur.

No problem until: Aneurysmal rupture, which can cause a stroke or widespread brain injury, which eventuates in cognitive loss and or speech problems. Big issue is not iq, it is survival if rupture does occur. A good neurosurgeon can save lives. And over the years, risk of normal pressure hydrocephalus, which can cause dementia.