Assuming the rest of the system's hardware was capable enough, it might work "reasonably" well, at least for a majority of today's games, though in some demanding titles you might need to adjust settings just to maintain framerates above 60fps. And while some less-demanding games might manage to take full advantage of the screen's high refresh rate, that's not going to be the norm for most newer titles running at relatively high settings. So a lot depends on your definition of "FPS issues", but I would expect at least some games to not run ideally, and that's only likely to become more common as games become more demanding.
Performance-wise, the G9's 5120x1440 resolution is like running a game across two 1440p screens at once (only without the edges that would otherwise be in the middle), and as far as size goes, the viewable area should be similar to a pair of 27" screens side-by-side.
The resolution actually works out to a little less total pixels than 4K resolution. So, you might look at reviews showing performance numbers for various games running at 4K (2160p) on an RTX 3070 to get a rough idea of what performance may be like. Keep in mind, most graphics card reviews will be running games at "ultra" settings, while "high" settings will often boost frame rates somewhat without affecting visuals noticeably, so that's an option. And of course, an increasing number of games support DLSS or other advanced upscaling routines, so those could also potentially be used to get more performance without affecting image quality too much, so long as you stick to the higher quality settings.