iPhone backup is way bigger than used space on iPhone

I've been trying to transfer information from my iPhone SE to an iPhone 13. Both have 128 GB of space. When I try to do it with quick start, it says there is too much stuff to transfer. When I tried backing it up, this happened:

I don't have 107 GB of stuff on my iPhone, but the backup is that big. This is how much space is being used on my iPhone:

Only around 20 GB are being used. Why is so much space being taken up by the backup? And how can I fix it?