Step 1:
Head to Creator Dashboard → Incoming Payments.
Step 2:
Press the Download Report Button.
Step 3:
Open the file in Notepad or another Software (VSC works best for me because it has no 1000 Results limit) and Press CTRL + F to open up the Searchbar:
Type your Plugin’s AssetID and check the a number next to it.
Congratulations, now you know the amount of downloads your Plugin has!
(Yes, this also works for users with a private inventory)