Ps4 Pro 1TB, but only 861.4GB?

Is it normal for 1TB to be sold, but the hard drive in the PS4 Pro only shows 861.4GB?

Yes. (…)

This is always the case, even with memory cards. Never actually have the full memory that says ^^

The information / designations of the manufacturers are not always accurate or intentionally chosen, which may result in differences in the calculation. See binary and decimal prefix.

Yes, since some of the software for the ps4 is already on it