nouveau is the open source driver, which is usually enabled by default, unless you install proprietary closed source NVidia driver.
If the 'OpenGL ARB' issue happens with both driver, it may be a 0ad problem.
About the longitudinal "shadows" issue with rc2, it looks like a mesa/nouveau issue (that can eventually be fixed in the driver) so if you want to contribute I would suggest to report it here: https://gitlab.freedesktop.org/mesa/mesa/-/issues