In Xfce this works in a different way. You hit a key combination and the window gets in a “resizing mode”, where you can press the left/right/up/down arrow keys to resize the window.
After you’re finished with resizing, you hit Enter to complete the action.
By default the key combination for this action is Alt+F8, but you can define a different one in Settings Manager → Window Manager → Keyboard (tab) and look for the Resize window keyboard shortcut.
I found F8 indeed, but i also watch the video on the site and i found out just a second ago that these exact shortcuct actually also work in xfce the only need to be assigned to the correct shortcut in the the window manager/keyboard (Tile window to the top/bottom/left/right).
Your asnwer on resizing was correct, i just dit not phrase the question right
Hoping this also helps others. Thanks for the reply.