Easiest way to tell is: if your unit has knobs and dials instead of a touch pad, it's pre-2019.
The handle attaches low on the unit right above the wheels into pre-drilled holes. I never investigated a way to attach it to my pre-2019 MINI, but I did take the cord reel that came with my MIDI-I (post-2019) and attached it to my pre-2019 MINI because the holes matched up for that. The cord reel frees up a good amount of space in the hose garage.
Also note that when you get the telescoping handle, you have to remove the cord wings from the back of the Dust collector before you install the handle. My Midi was bought in 2020, and it has the Bluetooth and TouchPad.
Yes, Festool 203722, available at your favorite retailer of choice.
Some have posted that you need to scribe the unit to make it fit on the older MINI/MIDI, but I just bolted mine straight up. The threads are coarse enough that I'm not terribly concerned about it flexing or breaking loose. Also, I was in a hurry and not feeling particularly enthusiastic about scribing it.