Shu”a says mesholim umelitzim, stam stories; nothing inappropriate. The proof is that the next words are if there are divrei cheshek, then it’s assur for another reason in addition to moshav leitzim, and shu’a gives the example of some romance book called sefer emanuel(which I’m sure was relatively tame by 21st century standards).
The rema doesn’t allow “war stories”, he mentions specifically Josephus because it’s Jewish history, which is valuable since it teaches emunah.