@njhorseman
Yes, I agree @Ferry_Watcher is a wealth of cruise information, particularly for Pier 91. This from their previous post which indicates embarking passengers are dropped at the terminal. It does seem to deviate from the Port’s website although I’d like to get a confirmation from Ferry_Watcher. It’s from 2019 so things may have changed. Did you see a more recent post from them?
“The Uber/Lyft area is just used in the mornings for passengers disembarking. All passengers arriving to embark (Uber/Lyft, bus, private car, town car, etc) are dropped off in the driveway area close to the Terminal 91 building.”
This map may be out of date as well but is on the Port's site but indicates the ride share lot is for pick up.
https://www.portseattle.org/sites/default/files/2021-08/Terminal 91 Map.pdf