Apple - Lost the Option to Boot into macOS After Windows 10 Bootcamp Installation

If you have access to Windows only I'd suggest you to try these steps:

1. Access the run command via Win + R (I don't know how Bootcamp actually remaps Win key, alternatively just open start menu and type run).
   

2. Insert msconfig once inside the Run GUI.
   

3. Once accessed the System Configuration Utility click on the Boot tab.

4. Check the option No GUI boot and click OK.

5. Now you have to Restart and hold down Option key.

You should now see Mac OS and Recovery as boot options. Enter Recovery --> Startup Disk, now you may be able to select you default boot drive.

If you have Filevault enabled, one way of making the default boot drive selection option appear is to change the Boot Security from High to Medium or None back to High. It will then prompt you to enter your password so it can check to confirm that the encrypted drive is bootable. Then you can select the partition and choose to boot from it.

Now Reboot as you would normally(without pressing any key while you're doing it) and you should boot automatically inside Mac OS, from there I'd create a new Bootcamp instance.

Your disk is not FileVault encrypted. It was decrypted to be resized for Windows' partition and is now attempting to background re-encrypt. FV progress is literally ---- or nothing but Conversion Status:Converting. However the extents ARE successfully encrypted and thus CS sees it as a FileVault partiton. The problem I'm almost certain is from buggy CoreStorage implementation, mainly because CoreStorage is incredibly unfinished... and the fact that BootCamp Installer likely does not know how to treat a FileVault drive that is mid-encryption... on a CoreStorage LVM partition... that it as an MBR/FAT/NTFS based loader needs to resize. I suggest you don't try to layer all these technologies on top of each other in the future. FileVault is especially hard to fix if it get's nuked mid-encryption.

Try this before attempting to go further to pull the CS partition out of FileVault.

sudo diskutil unlockVolume 09CCCB6E-6693-4EBB-AA17-D8F91A1DF5C2

use the password for the FV partition then,

sudo diskutil cs revert 09CCCB6E-6693-4EBB-AA17-D8F91A1DF5C2

to disable CS, it may take some time.

You should be able to then use standard Disk Utility tools to repair and disable FileVault. You should do this as soon as possible (even if you want to re-enable it later) as your issue is almost certainly down to encryption issues. In the future be very careful with your system in the days after you enable FileVault. It encrypts your drive in the background and sudden power losses can lose you your data.