The problem is that modern or especially futuristic warfare is inherently complex when compared with fantasy or historical warfare. Using modern warfare as an example for the sake of familiarity, you have a wide range of different arenas of combat that all have fundamentally different rules with little overlap but yet all are more or less required. Submarine warfare has almost nothing in common with mechanized infantry tactics which has almost nothing in common with an air campaign. While some systems might be made obsolete, it seems unlikely they could ever be replaced by something that would manage to truly simply warfare in the sense that it could become more like a fantasy setting in this respect.
Major franchise examples seem to mostly fall into one of two camps, as exemplified by two of the largest overall examples. Star Trek imagines a future in which space battles utterly dominate under the idea that ground battles don't matter if one has orbital superiority. Ground combat is limited to small groups in what is more accurately called a shootout than a battle. However, modern American police SWAT teams are better armed and equipped for a violent encounter (at least having stun grenades and body armor as well as rifles or SMGs as the standard). I’m not sure if this is more an indictment of American law enforcement or the military effectiveness of most military powers within the Star Trek galaxy. Most other science fiction settings fall into this same camp, as while examples like BSG or The Expanse seem to have somewhat more practical ground armies, they still largely seem to have adopted the model that ground warfare is mostly irrelevant beyond small scale operations.
The other prototypical example is given by Star Wars. While most groups have a fully equipped military force, it is one in which a simpler WW2 or earlier style of combat dominates. While they reference electronic warfare and do seem to use guided weapons, it is done to justify attacks that have more in common with visual range WW2 air battles and torpedo bombing runs(or the dam busters for the thing that was literally the direct inspiration). On the ground, we see proper combined arms occasionally but they still often find themselves in a mix of trench warfare and using massed infantry tactics a la Napoleon. When they do use armored vehicles they seem more akin to infantry tanks than true maneuver warfare given that their walking tanks generally move at a human walking speed. The only real modern element of their planetary warfare is a reliance on air mobility when there aren’t shields in the way. A similar reliance on air mobility with limited combined arms is seen in cases like HALO.
So are there any reasonable ways to simplify warfare in SF settings other than just ignoring the actual complexity?