LXQt does not allow to easily resize.
I created some shortcuts that allow to resize a windows easily
$ kate .config/openbox/rc.xml
Then add under <keyboard> the following:
<keybind key="C-S-KP_4"> # Left
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo">
<width>50%</width>
<height>100%</height>
<x>0%</x>
<y>0%</y>
</action>
</keybind>
<keybind key="C-S-KP_6"> # Right
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo">
<width>50%</width>
<height>100%</height>
<x>50%</x>
<y>0%</y>
</action>
</keybind>
<keybind key="C-S-KP_2"> # Up
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo">
<width>100%</width>
<height>50%</height>
<x>0%</x>
<y>50%</y>
</action>
</keybind>
<keybind key="C-S-KP_8"> # Down
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo">
<width>100%</width>
<height>50%</height>
<x>0%</x>
<y>0%</y>
</action>
</keybind>
<keybind key="C-S-KP_7"> # UpperQuarterLeft
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo"><x>0</x><y>0</y><height>50%</height><width>50%</width></action>
</keybind>
<keybind key="C-S-KP_1"> # LowerQuarterLeft
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo"><x>0</x><y>-0</y><height>50%</height><width>50%</width></action>
</keybind>
<keybind key="C-S-KP_3"> # LowerQuarterRight
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo"><x>-0</x><y>-0</y><height>50%</height><width>50%</width></action>
</keybind>
<keybind key="C-S-KP_9"> # UpperQuarterRight
<action name="UnmaximizeFull"/>
<action name="MoveResizeTo"><x>-0</x><y>0</y><height>50%</height><width>50%</width></action>
</keybind>
Finally run
$ openbox --reconfigure
