An error occurred while saving the commentKiviuq commented
You'd expect more in 2018. Typical. A workaround if you are technically inclined is to make a directory junction.
For example, let's say our games are in G:\Games and Twitch wants to use "C:\Program Files (x86)\Twitch\Games Library".
From an elevated command prompt:
Create a folder G:\Games\Twitch - mkdir G:\Games\Twitch
Then create a symbolic link between C: and G:
mklink /j "C:\Program Files (x86)\Twitch" G:\Games\Twitch
This way even though Twitch is "pointing" to "C:\Program Files (x86)\Twitch\Games Library" Windows will put the files into G:\Games\Twitch\Games Library"
Not perfect but at least something.