System data too large

I have an iPhone 12 mini running iOS 18.5. I don't do much on it, just 2-3 games, WhatsApp, social media, Spotify, and other common apps (about 20-25GB in total), which is why 64GB of storage is usually enough for me. For the past few weeks, I've had the problem that the system data is filling up the storage with up to 30GB, to the point where I have less than 100MB free, and apps such as WhatsApp no longer work.

Why on earth does the system data take up almost 50% of the storage, and how can I fix this?