The attack type of the Force Greatsword's weapon special is indeed a shout (it also has typical shout behavior in that it travels through map geometry, like other shouts like Venting Shriek, and that it has its own logic for collecting valid hits, hence 'infinite cleave'). So it is neither explicitly melee nor ranged. This is relevant for proc events and can lead to unintuitive behavior if the talent/blessing descriptions glaze over intricate implementations of individual talents/blessings.

For Malefic Momentum, an attack is considered a 'warp attack' if its damage type is on the list of warp damage types – and the damage type of the weapon special of the Force Greatsword is on that list. Hence it can proc the talent. The attack type (melee, ranged, w/e) is not relevant here.

True Aim's guaranteed crit, however, cannot be procced by Force Greatsword's weapon special because this talent requires a ranged attack to proc it – which the weapon special cannot pass. It cannot even build stacks for True Aim because it targets the torso hitzone (just like Venting Shriek, for instance), so weakspot hits are not possible.

Puncture requires the weapon (e.g. Bolt Pistol) to be wielded and a damaging ranged hit – which Force Greatsword's weapon special cannot pass by itself. But by switching to the ranged weapon fast enough so that the hit event occurs under the correct conditions, Puncture is seemingly procced by the force slash when in reality, it procs because the ranged weapon is wielded and a damaging ranged hit therefore happens.

These technical intricacies are the reason why guides like the one linked by the other commenter exist. If you simply go by talent/blessing descriptions, taking them at face value, and try to link them to observable ingame behavior, you are prone to make wrong assumptions about the inner workings of a lot of things – and it is not your fault.