How to get more purgeable space

I recently upgraded to 10.13.4 and really want to get Windows 10 on through Bootcamp assistant. I have a macbook pro with 128GB of space. Recentley I have been transfering data elsewhere to free up space for Bootcamp. Bootcamp says I need 40GB and I have around 60GB but it still wont let me start the process.

I think this is because it has to be 40GB of purgeable space, and I have no idea how to increase that. I have done multiple things such as sharing files to the cloud and the other optimization settings. Can anyone please help me find 40GB of purgeable data so I can get Windows.