Nothing against closed source though. For example, I enjoy x-plane a lot which while not free (in either sense) of course has a large community providing both free and non free add-ons. This seems more of a game with a focus on combat and less on realism or looks.
An actual free, open source flight simulator that deserves mentioning is Flightgear. I've played with that a couple of times but always end up reverting to x-plane. But flightgear has some nice features and also a nice community. It just doesn't look and feel anywhere near as good as x-plane (which is a tall order because it is very good).
Anyway, I checked out some footage on Youtube. Visually, it has nothing on even Flightgear; which I'm pretty sure probably has some combat mods. Or even any version of that the last few decades or so, actually. It actually reminded me of some dos games I used to play in the early nineties. E.g. Jetfighter II (released 1990) was pretty awesome back in the day. It looks like that but with higher resolution. But e.g. the ground is a featureless green blob; just like in Jetfighter II, and clouds are white polygons hanging in the sky, etc. And Jetfighter II had a HUD that was about as feature rich as the one in this game. Of course it was way more pixelated than this. But they even managed a cockpit panel :-). I wouldn't call it photo realistic but it didn't look half bad for the time. There are probably better/later game that this thing is shooting for. But I just never really got into combat flight simulation.
I guess they are trying to recreate some of that experience. Not that it matters; but I guess the gameplay is more important than the looks for this. Actually looks like it could be a lot of fun.
BTW. I have nothing against MS Flightsimulator. The latest version looks great. But I just don't have any windows computers anymore at this point. Combat is not really something either of the other flightsims I mentioned are made for or even good at.