Mojo gain Just Dance 2019 is the same as 2018. You only receive 30 Mojo from dancing offline and 45 Mojo dancing on the world dance floor, no matter your score. You'll need over 200,000 Mojo to get all the gift machine rewards. Because of that, the same method from 2018 works for 2019.
Now here's how to passively grind it out before this game goes offline. You'll need a phone you don't really use and a fan or similar device. Like those Honeywell Turbo Force Table fans that go for $15 to $20 at a Target or Walmart.
Start Just Dance 2019. Pick Phone tracking. Go to World Dance Floor. Turn your fan on and have it point straight up. Plug the phone into a charger and place it centered face down on the fan. The vibrations on the fan should be enough that the game will score the phone as Good or OK for most moves. If it doesn't work, put a piece of paper in between the fan and phone since the paper shaking might help the vibrations. Wait until the next song starts and see if it still gives points to the phone. And voila, passive Mojo. Don't forget to check the game every once in a while to make sure the phone is still "playing".
Doing this method, you can also pick up these achievements
You'll get about 1 level every hour or so with this method since xp gain is based on your score. So if you're starting some scratch, about 100 hours of passive phone playing time.
In addition, I recommend you also go for this achievement
The best Challenges for this method are "Play X amount of Solo/Duo/Trio/Quartet songs", "Get X stars", etc. Challenges that don't require actual effort to get. If you don't have any progress in a Challenge, it will change to a new one when you restart the game. One method of quickly changing challenges is this:
Start Just Dance 2019. Pick Kinect Tracking. Your challenges now appear. If you want to change it, go to World Dance Floor. Press the XBOX Guide button to open the guide and then again to close it and get back in the game. The game will say you've been disconnected and kick you back to the title screen. Pick Kinect Tracking again and it'll give a new set of challenges. Repeat if you want new challenges. If you get good ones, back out to the title screen with the B button and pick phone tracking and then use the above method to grind it out.