Just opened the FSDT Installer and now shows that I have FSX P3D Installed (which I clearly don't) instead of MSFS, no way to revert back to MSFS so for now I'll have this product uninstalled from my computer. It is unfortunately not stable as of [SEP1]
Nowhere the installer is saying anywhere you have "FSX/P3D Installed". The installer will just show which FSDT product it knows about, for any simulator, and you are allowed to see them and possibly Activate them even when their simulator is not even installed, because which simulator you have is completely irrelevant to the scenery activation status, or the ability for the installer to let you get your lost keys for a product, which you might want to use even BEFORE installing the sim. That's why is entirely correct the installer would still show FSX/P3D products, independently from the installation status of the simulator they belong to.
What is REALLY happening here, is that you have clicked on the MSFS 2020 logo, the one which now shows "Products are hidden", because that what clicking that icon does, as you can see from the P3D icon which says "Click Here to Hide Products".
So, you clicked on the MSFS logo which said ""Click Here to Hide Products" (when it was active), and the program complied with your command, so it HID the products, as you asked.
They'll reappear if you click the MSFS logo again.