Bitlocker is blocking me from partitioning my drive – can't dual boot because of it

My PC's about 7 years old and starting to slow down, so I wanted to try Linux. But I still need Windows for school, so I figured I'd set up a dual boot.

Problem is, when I tried to shrink the partition, Bitlocker blocked me. I've been looking for a fix but haven't found anything that actually works.

Disk 1 in the screenshot is just a USB drive, not the main one.