The new ease with which panels can be docked in the monitor is to a good idea, however you can’t prevent them from docking when dragging the window over the monitor.
It’s OK if you have a dual monitor setup, but it’s a pain on single monitors, so for instance you bring up the slave reports panel, and it sits on top of the monitor just fine, but as soon as you drag it you can’t stop it autodocking.
Can it default to having to press shift or control to enable docking?
I believe the intended workflow is to engage the Lock Panels icon when you have your panel layout the way you like it, and only disengage it temporarily when you intend to dock a panel. This way, any new panels opened would always float, and you have to explicitly allow docking by toggling the icon off before docking, and then on again to prevent it for future new panels.
With panels locked, you can still resize the UI, but cannot accidentally dock a panel. However, due to (I believe) a peculiarity of Qt, it is still possible to accidentally undock a panel by double-clicking its title bar.
I suspect that the current behavior is easier to discover by first time users than knowing that a key has to be held to perform docking, but I am not involved in those design decisions, so I am just providing a possible workaround… 