Depends on the type of suspension and the how the rebound is damped…very easy to do that with a suspension fork, harder to do with something like a seatpost.
But I think the differences we are talking about here are so small that they are meaningless compared to the increased comfort.
I have been riding a suspension seatpost for years on any rigid off-road bike I have…hardtail MTB, CX and now gravel. Unfortunately my 2 decade old USE seatpost gave up the ghost this summer (bushings crapped out) so I am now on the stock Cervelo SP. I can’t detect any increased efficiency, but I sure miss the extra comfort.