Does FileVault 2 encrypt unused space when expanding an APFS volume?

itservicesx wrote:

I understand that if I create a Windows partition through Bootcamp Assistant on my Mac running macOS Catalina (in APFS), my APFS container will shrink to make room for the Bootcamp partition.

Correct.

However, if I later decide to delete my Bootcamp partition through Bootcamp Assistant, my APFS container should re-expand to fill up the space.

Correct.

My question is - if I have FileVault 2 enabled on one of the volumes in my APFS container, and then I delete my Bootcamp partition, when my APFS volume expands, does FileVault 2 immediately encrypt the new unused space that used to be in Bootcamp, or does it remain unencrypted?

If the APFS volume expands and uses any of the space that is available within the Container, the contents of the Volume will be encrypted. Encryption is based on Volumes, not disk space. If it remains unused space in the Container, encryption is not necessary.

Do you have a specific concern regarding encryption?

Excellent!