I have an Apple Watch 5 unlocking on my 5,1 , in both high Serra, and Mojave , I have not been able to do so in Catalina.
or even get Catalina to recover from sleep at all without reboot for that matter, but I digress.
my blue tooth is the 4.2 type, not 4.0.
set up was a pain, and took so many paths to get this working, I don't remember it all...
however I assure you it does work.
here is Mojave 10.14.6 and Apple Watch 5 on 6.2.6, unlocking my 2012 5,1 Mac Pro.
I wonder if bluetooth 4.2 is key?
I never used CAT.....
Bluetooth Low Energy Supported: Yes
Handoff Supported: Yes
Instant Hot Spot Supported: Yes
Manufacturer: Broadcom
Transport: USB
Chipset: 20703A1
Firmware Version: v168 c4824
Bluetooth Power: On
Discoverable: Off
Connectable: Yes
Auto Seek Pointing: Off
Remote wake: On
Vendor ID: 0x05AC
Product ID: 0x8294
HCI Version: 4.2 (0x8)
HCI Revision: 0x12D8
LMP Version: 4.2 (0x8)
LMP Subversion: 0x21A8
Device Type (Major): Computer
Device Type (Complete): Mac Desktop
Composite Class Of Device: 0x380104
Device Class (Major): 0x01
Device Class (Minor): 0x01
Service Class: 0x1C0
Auto Seek Keyboard: Off