I suppose in any realistic scenario we should assume that the enemy may be listening to all our communication at all times. This is the assumption behind such daily things as WPA3, SSH, TLS.
Yes, so all in all for satellite vs. fiber in backbone applications, I'd say that it's a wash (or slight win for fiber) when it comes to security, and a definitive win for fiber when it comes to jamming resistance.
In the field it's a completely different story, of course – you can't always pull fiber (although it does appear in unexpected scenarios, such as fiber-operated UAVs or torpedoes).
Wire-guided drones and missiles seem to be increasingly common, probably due to the cost of instantaneous radio jamming being so low - that's a short-lived signal that is going to a vehicle near your adversary. Torpedoes make a lot of sense for other reasons because radio has a very hard time getting through water (and things like sonar have too low bandwidth as well as giving away your position).
However, it's very easy to cut a fiber in a way that is hard to repair. Fishing trawlers do this all the time. In that sense, fiber can be "jammed" (sabotaged) much more easily than radio/satellite.
I suppose in any realistic scenario we should assume that the enemy may be listening to all our communication at all times. This is the assumption behind such daily things as WPA3, SSH, TLS.
Jamming is a much more serious concern.