Let’s continue with practical fixes. This post is intended for users with existing Bumblebee installation. 1st time installations will not have this issue.
If Bumblebee was installed recently, by following Antergos Wiki article, then it may fail to run Steam with optirun prefix. Steam hangs forever and never finishes to load. It’s impossible to execute Steam on the discrete Nvidia card (on Nvidia GPU). There were some posts in the forum reporting this problem, some time ago.
Again, the issue is caused by changed default dependencies. One of the support packages, automatically installed in the past, is not installed the same way anymore. Simply install it by hand:
sudo pacman -S lib32-virtualgl
Steam will start on discrete Nvidia card without a problem now: