I take back what I said about
You don't need to go through the rest of the notarization process for Steam builds.
It seems that you
do need to at least go through step 2.
If you don't go through step 2, then the signed .app from step 1 will give the error "Unnotarized Developer ID"
Step 2 doesn't change the .app, but it does give Apple information about the build which it needs in order to verify the .app file.
In any case, I've still been unable to get this working. I don't think SteamPipe is able to handle notarized .app bundles right now.
steamcmd doesn't appear to run on Catalina at all (throws a warning on Mohave, refuses to start on Catalina), and a notarized .app bundle fails verification after going through SteamPipe (even if it's uploaded from Mohave, without moving or changing the bundle in any other way).
Unless Steam changes something in their build tools, I think only hacky workarounds (like uploading a DMG and having a shell script extract it) will work right now. But that would probably fail Steam's verification anyway...
Finished games
-My games: Sickness, Wander No More, Max Massacre, Humanity Must Perish, Tomboys Need Love Too, Sable's Grimoire, My Heart Grows Fonder, Man And Elf, A Dragon's Treasure
-Commissions: No One But You, Written In The Sky, Diamond Rose, To Libertad, Catch Canvas, Love Ribbon, Happy Campers, Wolf Tails
Working on:
Sable's Grimoire 2
Scratching my head over this entire convoluted process, thanks!