Copy poses and paste them as X-flipped Pose; How to ?

Hi all,
I am not proud of asking this basic question but I can’t find how to do this :
I know Blender allows to copy poses and paste them as X-flipped Pose within one frame provided bone names conform to the naming convention. I think this is what I need since I want the right arm to pose as the left arm and vice versa. But how do I do that ???
Thank you for your help

When you are in pose mode, there are some icons of clipboards all the way at your right. The left one copies pose. the middle one pastes the same pose. The right one pastes the flipped pose. Flipping poses makes things so much easier!

Remember also, that the bones must have the correct naming convention for blender to identify them as left/right. You need your left bones’ names ending in _L, and your right ones in _R. A dot is also a valid separator.

Thank you ! Amazing. Bone naming was right.
But the pop-up text is somehow not clear about the X-mirror since both Paste and Paste+X-mirro have the same text, unless you look at the python flipped status

Thank you for your help