Hi there, thanks for reaching out.
The reason why the Note 20 Ultra can’t work with Juice 2 is that the phone is too big to be compatible.
As you can see in the following pictures. The camera is partially blocked by the Juice.
Besides, since the phone can’t seamlessly stick to the Juice, the magnet is not strong enough to enable your phone to slide out the groove with the Juice, or wirelessly charge your phone steadily.