The libre driver is included in Linux (and Linux-libre), so you wouldn't have
to install it. That driver is Nouveau, and the Nouveau website has a page
documenting support for the various features of the cards:
https://nouveau.freedesktop.org/wiki/FeatureMatrix/
In general, the standard advice if something doesn't work is to try the
latest version of Linux-libre (jxself supplies one here). If that doesn't
work, you'll have to wait a few years for Nouveau to catch up, remove it and
use integrated graphics instead (good choice if you have an Intel CPU, not
any use if you have an AMD CPU), or replace the card with an older model that
Nouveau supports.
By the way, regarding whether or not being a "product" exempts games from
needing to be libre: if that were the case, that would exempt Windows,
Microsoft Office, the various Adobe programs, etc. These are all considered
to be "products", too. The simple fact is that just as they are proprietary
software, proprietary games are proprietary software.
I suggest you should never financially support proprietary game developers,
and instead support development of libre games. You can do this by supporting
crowdfunding campaigns (such as my recent campaign for Hexoshi), or by
donating to projects/developers you like.
