Is CiviHR still active? This extension looks really interesting but the last release is almost 3 years-old.
As far as I know, they had too many issues with the more recent versions of CiviCRM so it's no longer supported. A client of mine had a chat with Jamie @ Compucorp last February (2020) at the CiviCamp and the message I got from my client is that they were no longer supporting it. I don't know the details so you'd need to speak to Compucorp for more info