The code I offered in this thread (based on the code of others, I hasten to add) fundamentally works:
https://forums.creativeclouddeveloper.com/t/sp-menu-backround-clipping/7693/7
Revisiting it just now (I thought I had better check the code still worked), it may be that you can’t use an sp-menu and sp-menu-items within the sp-popover because the text in the sp-menu-item does seem to be clipped to the panel edge (or it needs some extra css to work), but the popover is definitely extending beyond the bounds of the panel edge (which is what you have asked for), as you can see when the sp-popover contains this crude code:
<div style="background-color: grey">
<div style="color:white; font-size:12px; padding:4px">Do something</div>
<div style="color:white; font-size:12px; padding:4px">Do something else</div>
<div style="color:white; font-size:12px; padding:4px">Do a third thing</div>
</div>
resulting in this:
I’ll be interested if you find a way to have a context menu popup where the mouse has been clicked in the panel.
Philip