I want to play a game in an older update, but can’t see a way to choose a specific version. Is this possible?
Megos answer isn’t entirely correct, it depends, so I’ll expand a bit.
In general, as Mego says, there is no way to do this, but some publishers do provide this option.
For example, the Paradox Grand Strategy games offer the option to roll back to any prior version and play that.
The only possible mechanic to do this is the beta program. Originally this was provided to allow users to opt into a new patch before it was released, but it also got adapted to provide roll backs.
Right-Click your game of choice in your Steam Library. Select Properties, select the Betas tab.
Click on the drop down menu at the top, which should say “NONE – Opt out of all beta programs”.
If this menu now offers earlier versions, then your game offers the rollback function you seek, otherwise there is nothing you can do.