diskutil list command output in terminal shows that recovery partition is not available:
It may be also possible to boot into recovery and it may have a different version than the OS itself.
Recovery partition does not exist or macOS is not able to see it.
When macOS is not able to see "Recovery HD" partition, it will not be possible to enable FileVault.
Run Internet recovery to install the current or latest allowed version of macOS on the affected Mac.
Re-image Mac with the image that includes recovery partition.