Can't speak for "modern fighters" but the Tornado GR1/4 has a pretty good AP because it was designed to fly an entire route at low level, on Terrain Following Radar with the AP engaged. The autothrottle can maintain a selected groundspeed. The AP can fly a route at medium level but has no vertical nav function and cannot fly a procedure of any sort. I believe auto ILS was envisaged but never cleared for use.