There is a console built into Steam that lets you downgrade games (among many other things) even when the developer doesn‘t offer older versions officially through the regular launcher. This is only for extreme cases were you really really just want to keep your mods or an update doesn‘t work on your machine because you will have to redownload the entire game. There are online tutorials that explain it and each version for each game has a unique ID that you need in order to download it. So there is always way but it‘s clear the platform doesn‘t really want you to use it or know about it.