I’m not sure how to paste directly into a pane, but you can copy by opening up the scrollback in EDITOR from search mode using Ctrl+S e. This creates a file in /tmp so I try to make sure to clear it when I’m done.
I usually only copy and paste between editor windows using a script that mimics xclip (automatically used by helix), and if I need to paste a command I either edit my bash history or write a script.