Never download Flash Player from anywhere but the Official Adobe website or from within System Preferences > Flash Player > Check for updates. There are many bogus Flash Player installs that will install malware.
Update Your System Software. Before we do anything, let’s make sure your Mac is up to date. 2 days ago I'm planning on doing a clean install of Big Sur sometime after it is released. I was reading Apple's help articles to see what their documented steps were, but I'm confused on their first two bullet points about How to choose between APFS or Mac OS Extended. I'm currently using Catalina.
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Mac Cleanup Pro is not Apple. No Anti-Virus software or so-called “cleaning” apps are needed or recommended for Mac OS. They can conflict with Mac's own built-in security. At best they will slow your Mac by using unnecessary resources and at worst will bork your entire system.
If you think you have installed malware run Malwarebytes. Malwarebytes was developed by one of our own colleagues here in ASC and is about the most proven anti-malware software for Mac.