Author answered in the comments [1]:

> You can use a pilum as a thrusting spear, but it isn’t particularly well designed for the role (weight distribution is all wrong, the long shank is fragile (bends) in ways you don’t want, etc). If the plan was to do that, you’d just do what most Gauls and Spaniards seem to do: carry one javelin and one thrusting spear. And in the event, our sources are quite consistent that when they imagine Roman heavy infantry in close combat, they are using their swords, not the pilum. So while that’s a possible use and it probably happened from time to time, I don’t think it was a normal use.

[1] https://acoup.blog/2023/11/24/collections-roman-infantry-tac...