Install from the .dmg

The install command on the download page needs none of these steps.

oxob is not signed by Apple yet, so macOS blocks its first start once:

Open the .dmg and drag oxob into Applications.
Open oxob from Applications. macOS says it could not verify oxob: click Done.
Open System Settings → Privacy & Security, scroll down to Security and click Open Anyway (it shows for about an hour after the block).
Click Open Anyway once more.
Confirm with Touch ID or the password.

Open Anyway needs an administrator's password. On a standard account, use the install command: it needs none.