Hi guys, just posting to let you know about the existance of an archived copy of the latest build of Steam from last year. It might be a good idea to add it your personal backups. It has a steam.cfg file with settings to prevent further auto updates. Hope it helps!
https://archive.org/details/steam_201901
https://www.reddit.com/r/Steam/comments/abtw53/steam_build_nov_26_2017_archived_for_xpvista/