I installed a new C drive and reinstalled Windows, can't enable bitlocker

I recently bought a new 4 TB SSD for my system drive because I needed more speed and space. I installed Windows on it but now realize I made a mistake by not removing the old Windows drive first.

In the screenshot disk 5 is the original Windows drive, which has since been formatted and now used for data, and Disk 4 is the new Windows drive.

When trying to enable Bitlocker I get this error.

I tried to fix it by creating a 500MB partition, but it got formatted as a 499 MB partition and running

bcdboot C:\Windows /s B: /f UEFI

but I still get that error message.

I've installed all my apps and data now, so I don't want to reinstall again if I don't need to.