So I'm assuming I need to buy 2023 Premium if I want the new features?
Yes, for the new features only that are not included in the Free Edition, and there aren't many. See the comparison chart. Look at the Free column to see which new features are included for free.
Isn't there an upgrade option?
Of course. If you want to purchase the 2023 Premium Edition, select Upgrade.
If you just want Music Maker 2023 and the new features that come with the Free Edition, download and install the Free version/Edition. After logging in, you will have everything that you had before and more. I suggest that you do this first and decide later if you want the 2023 Premium Edition. If you purchase the Premium Edition later, you simply have to activate the serial number on the Welcome screen, no need to reinstall the program (which is Free).