Just a hint, if you happen to change your PC motherboard for an AsRock, in my case a AsRock B365 Pro4, and can witness the fact that the mouse remains powered even when the computer is turn off, just make this change to the BIOS :

- Reboot and hit F2 on the keyboard to enter the AsRock BIOS
- Advanced
- Chipset
- Scroll down to DeepSleep
- Switch from Disabled to Enabled in S5
- Save and Exit

Problem fixed !



For the record, Sleep states are :
S3 = Sleep
S4 = Hibernate
S5 = Shut down