So I haven’t posted here (or anywhere for that matter) for quite some time, but still lurking around, currently trying to do unorthodox things to my new Steam Deck.
Picked up a Humble Bundle which has a few duplicates I already own, so Steam keys for those games are below - please post if you take one & I’ll cross it out.
The Secret of Monkey Island: Special Edition
AW4FB-V0VLJ-X4H9F change the first letter to H
Monkey Island 2: Special Edition
AJW8L-90YFI-560GX change the first letter to J
Star Wars Knights of the Old Republic
AHJ5M-H5TWY-W8CKI change the first letter to H
Star Wars Jedi Knight - Jedi Academy
AWA50-3YCPH-IWNQD change the first letter to H
Star Wars Republic Commando
A4XEA-6VTC0-HWRNV change the first letter to I
Enjoy! A generous soul here gifted me something on Steam or GOG way back in the day, so I’ll belatedly pass that on.
----edit–
Found a few more I have on Humble, as below:
Limbo
APD0X-F0E3I-ZW23H change the first letter to N
Psychonauts (excellent)
ABTJK-FWA54-64WMZ change the first letter to X
Psychonauts on GOG.com
ANRT005D8D74D3C896 change the first letter to B
Those ones are older so might have expired? Who knows… 
----edit 2 - cunningly encrypted the keys following @the_borderer 's good suggestion