Welcome to Android Central! I edited out that link, since it's not really important which app you installed to try to help (and, in fact, apps that claim to "optimize" your phone will sometimes make things worse, because they basically just kill apps in the background repeatedly).
First of all, what kind of slowdowns have you seen? Does it still seem sluggish if you boot into Safe Mode?
https://www.androidsettings.net/xiao...e-8-safe-mode/
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