MacBook storage issue

How can I fix my MacBook's storage issue? (System Data taking up too much space)

Hey everyone,
I’m having a pretty frustrating issue with my MacBook Air (2017, macOS 12.7.6, 8 GB RAM, bought new in 2020). Maybe you have some advice?

Here’s the deal: A few months ago (mid-2024), I had over 50 GB of free storage. Now I’m down to just 26 GB, and I can’t figure out why. I don’t think I’ve downloaded enough to explain the massive drop in available space.

I deleted an iOS backup today (6 GB), but the free space didn’t increase. That’s the only time I’ve noticed this happening. Otherwise, the system does seem to update storage when I delete files. I’ve restarted the MacBook, but the issue with the backup storage persists.

Here’s what the Storage breakdown looks like:

• System Data: 25 GB
• Documents: 20 GB (makes sense because I’m a student, but still surprised it’s this high)
• Apps: 16 GB (seems normal)
• iOS Backups: 8 GB (used to be 14 GB before I deleted the 6 GB file)
• Photos: 4 GB
• Music: 1 GB
• macOS/System: 15 GB

I don’t use iCloud, and I already contacted Apple Support once about this, but the issue persists. My main concern is that the 25 GB of “System Data” seems insanely high. Could this be a hardware problem?

Other details:

• I’ve had the MacBook for 4 years, no warranty anymore.
• I usually have over 100 Firefox tabs open (but I’ve had this habit for years).
• My university folder is over 10 GB, which makes sense for my work.
• Everything else seems normal, and the device works fine otherwise.

Does anyone have experience with this or know how to fix it? Should I consider repairs? Or is there something I’ve missed? Any tips would be super helpful!

Thanks!