Rivnuts from Homestead, PA on 8/2/2023 4:51:08 PM:
So, I rode into Pgh today in and around the area of the Amtrak Station looking for potential places to lock up your bike for a few hours after arriving in Pgh and before taking the train northward.
First, the thought of parking your bike inside the Amtrak station isn't feasible as the waiting area at the station is only open from 6:00pm until 7:45am. So if you arrive before 6:00pm the station is not open. That said, there is a bike rack in the parking area just beyond the waiting area entry door. It is under roof so not susceptible to rain. There is little, if any, pedestrian traffic there albeit some construction workmen nearby. There was a bike locked there today.
Another option would be to lock your bike up on the south side of Penn Avenue west of Tenth Street. (See Google Maps of downtown Pgh area.) There are several outdoor restaurants and bars along the street in that area where you can lock your bike with a fair amount of people dining there.
Of the hotel entrances, there is a place to lock a bike near the entry to the AC Hotel by Mariott on Smallman Street just a couple of blocks from the train station.
Assuming you remove your bags with their contents from the bike, I think the first two options above are your best bets for leaving your bike for a few daylight hours.
Perhaps other forum lurkers familiar with the downtown area will have some other suggestions.