The pictured trunk is badly damaged, but it's hard to tell how long ago the injury occurred. It might be worsening canker, an infection that tends to be opportunistic that takes advantage of a pre-existing wound or stress on the tree (such as from drought), or it might be old "buck rub" damage, where a deer rubbed antlers on the trunk and injured the sapwood (crapemyrtle bark is very thin). In either case, the heartwood may have advancing wood decay at this point, which is not treatable. Worst-case, the portion of the canopy this stem supports may eventually die off. The only recourse would be to cut that stem down to the ground and let a new trunk regrow in its place from the resulting suckers.

Pollarding can be a common practice in Europe (more so than in the U.S.), but even so, it's not a recommended pruning technique, as it significantly raises the risk of wood decay around the pruning point, and the regrowth of branches from the point of recurring pruning are poorly attached (compared to the original branches) and more prone to storm breakage. Pollarding also stresses trees and can make them more vulnerable to pest and disease issues. We see what may be a couple Crapemyrtle Bark Scale on the trunk pictured, but can't tell if they are alive or not. We have seen examples of severe ambrosia beetle infestation in other crapemyrtle trees that are heavily pruned. Generally, it's best (and may be more cost-effective in the long term, at least if you're paying to have it pruned) to just replace a tree like this that is too big for the space with another variety or species that better fits into the area.

Miri