screen flashes when waking up

Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click https://discussions.apple.com/docs/DOC-250000211

Well, at best your iMac is a mess which has been caused by the user installing worthless and potentially damaging apps including CleanMyMac and a third part VPN that does nothing.

The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy.

Please locate the developers uninstall instructions for CleanMyMac and the VPN app that has been installed and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac  and then restart normally. After you have completed the uninstall and restart in Safe Mode you need to fix the damage CMM has caused. How that is done is you will need to install Mac OS which will fill in the missing and damaged parts. In your case I see that Apple's security has been turned off leaving your Mac vulnerable.

Also, there is NO backup of this computer which is short sighted and a 100% guarantee you will lose data. At the VERY least you should be using Time Machine to backup, if you are not aware of TM then all it needs is an external HD to back up to, a dedicated backup EHD. The one many prefer is the OWC Mercury Elite Pro.

After you have done all of the above then you can install Mac OS by re-installing in the Recovery Partition (hold down Command + R on startup) and then click the Install Mac OS link and install. This will not erase anything however, it will fill in missing and damaged parts of Mac OS. That being step you should NEVER do any major action without a backup!!!!!!!!!

• The Capacity of a Time Machine backup drive should be about 2-3 times the capacity of the amount of data on your internal drive. To see how much you have stored on your computer click About this Mac (look under the Apple symbol in the upper left of the display) and click the Storage tab. For example if you have about 512 GB on the internal drive then a 1 - 1.5TB drive is fine.
• Mac Security is Apple's pre-installed security, so no it has nothing to do with a Firewall. A firewall can be turned on in Mac OS however almost EVERY router has a Firewall built in, by default the Firewall is turned on so that means it is 100% unnecessary to turn on the Mac OS firewall. Apple's security protects against malware, it does not require the user to do anything and automatically updates itself whenever it is needed.
• No, NEVER EVER update Mac OS (or any OS) to fix a problem. Doing so just make fixing an existing problem more difficult to fix.

When you install Mac OS it should re-install the security portion that CMM destroyed.