Arma is described as 'Experience true combat gameplay in a massive military sandbox. Deploying a wide variety of single- and multiplayer content, over 20 vehicles and 40 weapons, and limitless opportunities for content creation, this is the PC’s premier military game' and is a first-person shooter in the games category. There are more than 25 games similar to Arma for a variety of platforms, including Windows, Steam, Linux, Mac and Playstation apps. The best Arma alternative is Battlefield. It's not free, so if you're looking for a free alternative, you could try Garena Free Fire or DCS: World. Other Arma like games are Squad, Escape From Tarkov, GROUND BRANCH and Ready or Not.
Its like if you tried to compare real war and a game of airsoft. Arma is ultra realistic simulation. BF is just a shooter.