io.github.libtmux.Pane.Pane.select

>>> pane = window.active_pane
>>> new_pane = window.split()
>>> pane.refresh()
>>> active_panes = [p for p in window.panes if p.pane_active == '1']

>>> pane in active_panes
True
>>> new_pane in active_panes
False

>>> new_pane.pane_active == '1'
False

>>> new_pane.select()
Pane(...)

>>> new_pane.pane_active == '1'
True

await pane.select();