/dev/sda is the whole raw disk - you typically don’t want to directly interact with /dev/sda, unless you are partitioning or overwriting it. There are a few layers between that device and the files:

• raw disk - /dev/sda
• disk partition - /dev/sda1
• luks container - when unlocked, mapped to /dev/mapper/{name}
• ext4 filesystem inside the luks container, mounted somewhere like /mnt, /media, etc

You’ll need to find where that ext4 filesystem is mounted, and run the chown command on that. You can run lsblkand see a tree of the above hierarchy, with the ext4 filesystem’s mountpount shown in the right-hand column.

Makes you wonder who the hell was still running kaspersky in the US…