Time Machine shows 'computer sleeping' with new WD drive

I installed a new WD 10 TB hard drive as a Time Machine backup disk, formatted APFS.

I get the attached message. What does it mean? That the computer is sleeping and not in active use, unlocked with my password?

I have another hard drive as a Time Machine device (two is better, I've learned the hard way) and it doesn't have any problems.

Any advice will be appreciated!

Ed in Brooklyn