With File Vault active, it is even more nearly impossible to recover erased files, as encryption makes raw data unreadable and unrecognizable.
With SSD drives (if you have that), it is even more nearly impossible to recover erased files, as blocks are randomly scattered, and free blocks are deep erased some time after the Empty Trash command, when the drive itself deems it a good time to do so (TRIM and similar functionality), silently and without user interaction. Just having the machine on could have made the deep erase happen.
With the new APFS file system (High Sierra and later), it seems impossible to recover anything, under any circumstance.
The lesson here is to always have backups, even more so with newer disk technologies. The old undelete tools are becoming obsolete, as well as the recover specialists.