I don't have that in the 4.9.0-FC1 version from Flight. Must have been a last minute addition. … But probably: The rewards that have not yet been withdrawn?

Withdrawn? Withdrawn from where to where? I usually get a few dozen each epoch but the amount it's showing is much more and the actual 'rewards' is correct and updated.

For some reason, prior versions of Daedalus only show the total rewards (ever?) including those that have already been spent/withdrawn in transactions. This „unspent“ should then be the same you see in other wallet apps (which mostly do not show total ever, but non-withdrawn rewards).