(You could already create an iZotope customer account and register your product there at this stage, via the Ozone Elements serial number provided by our system, but you're not obligated to do so in order to be able to download the plug-in installer.)
I was able to install Elements, however I can't register it. I was able to install iZotope Neutrino as well, with their tool and I was able to retrieve the serial key from the store. Elements doesn't appear in the shop since it's part of the premium poroduct.
As a Music Maker Premium 2018/2019 customer, the serial number for Ozone Elements would have been e-mailed to you when you first redeemed your Music Maker Premium serial number (or purchased the Premium edition via the in-app store). So, please look for that e-mail again. Maybe make sure to check your spam filter, too. If you can't get your hands on it, please get in touch with MAGIX customer service, and they'll recover it for you:
(Unlike \"Neutrino\", Ozone Elements can no longer be listed as an item in the in-app store, for contractual reasons. So, that's why you wouldn't be able to use the same mechanism of bringing up the in-app store info page to look up the respective iZotope serial number at a later point in time. However, the serial is safely store in your account on the MAGIX server, if you ever need to recover it again.) 153554b96e