BIOS Password is supposed to be removed when device is:
Deleted
Device Wiped
Enterprise Wiped
Enterprise Reset
The BIOS Password is present on the UEM console.
So when you delete the device entry, you delete the BIOS password from console.
If i recall correctly, on Dell devices, the Dell command monitor allow you to get the bios password via powershell for example, you could store it in a sensor and escrow the sensor using API.