VTE 0.58 will deprecate the rewrap_on_resize API. 0.60 is planned to remove the configuration, forcing rewrapping to be enabled. The methods will remain for API compatibility, but will do nothing. Rationale: https://gitlab.gnome.org/GNOME/vte/issues/135 Please prepare your app for not showing the corresponding UI option if running against (future) 0.59/0.60 or newer.
(0.58 will be released in Sep 2019; 0.60 in Mar 2020)
Igor referenced this bugreport in commit e89a558479ba42e4613d821ba1d6f744782f0317 Do not show "Rewrap on resize" option for vte>=0.58 https://git.xfce.org/apps/xfce4-terminal/commit?id=e89a558479ba42e4613d821ba1d6f744782f0317
Thanks, Egmont, fixed!