Is it possible to delete several players from a flow in one go without confirming each and everyone one by one?
Select all the players you want to unassign in the left panel of Setup mode. You can shift-click a selection, or you can Cmd/Ctrl-click individual players in order to get a non-contiguous selection.
Then untick the flow in the bottom panel.
Thanks a lot Leo
Yes the relationships between flows, players, and layouts go both ways so you can always select whichever one is the most numerous then tick/untick the other; if you wanted to remove one player from lots of flows, you could select the flows then untick the player.