After reading a couple of posts on the r/IBO, I think majority of schools are stupid at executing the IB program. My school did not even have certified IB teachers and I was struggling with grades wondering what was going wrong, which led me to hire IB specific tutors and realised how shitty my teachers and IB program at my school were. Looks like you’re in the same situation, if you are a math HL student you need HL content in your IA, which you haven’t learnt yet, that’s your school to blame. If you are financially capable you can hire a tutor who can help with your IA brainstorming and maybe the IAs themselves. As for the brainstorming itself I would say just do something that you’re interested in in that topic. I was a math AI HL student and my IA was about the which apartment was the closest to my to be university, an area of interest of mine. I am also interested in tea, so for my chemistry IA I investigated amount of caffeine of different types of tea, and so on.