First, please read this post and give us ALL the information requested there, especially about the exact version and variant of MM you have; if you're not sure where to find this, check under Help>About.
We also need to know exactly what you are trying to add to your existing installation; the desire to add More Tracks And Formats in Music Maker 2020 implies that you may have a variant of the software other than Premium. If that is the case it is often cheaper to upgrade to the full Premium version rather than buying "add-ons" to, e.g., the Plus version.
I have MM 2020 Plus version 188.8.131.52. The problem is that when I try to import a MP3 it says I need to get More Tracks and Formats from the store which isn't an issue since I have 2 free feature packages. But its not in the store.
I have the feature installed and it still shows up in the Store, when you mouse over the tile it has an icon displayed which shows it has been acquired, if you hover the mouse over the icon you get a small message - as do all the other functions already installed.
I see the same listing in the Store as @Steven-Swanson shows and as @browj2 implies: clearly, I have those features installed but the "More tracks ..." does not show for me in the store??? See screenshot (running 184.108.40.206).
Edit: I really should read ALL posts more carefully!! John CB's comment about making sure "Show purchased items" is checked makes the "missing" tile appear.