iMac stuck in boot screen

Did you hold down the Shift key for up to 10 minutes when attempting to restart in Safe Mode?

If you are restarting in the Recovery Partition (hold down Command + R on startup until it boots) then open Disk Utilities first, run First Aide 2-3 times back to back and look for errors. If any appear your HD is damaged. If no errors appear, exit DU then re-install Mac OS and attempt to re-start. If it still doesn't work, there is hardware damage and you need to go to an Apple Authorized Service Provider to have it professionally diagnosed and repaired.

CleanMyMac is considered malware by most experience users on these forums. It has zero value as it does NOTHING that Mac OS cannot already do. I would STRONGLY recommend uninstalling it per the developers instructions. Mac OS does not benefit from nor does it require ANY third party antivirus, cleaning or any other types of "maintenance" apps. If simply kept up-to-date and otherwise left alone Mac OS performs reliably for years for most users. You install may have been corrupt due to modifications CMM may have done to Mac OS!

Sorry, please click PRAM and NVRAM Reset

Attempt to restart in Safe Mode per the direction in Use safe mode to isolate issues with your Mac - Apple Support . Please pos back with the results.

Please reset the NVRAM.

Your welcome, likely a corrupt install.

Good to hear, sorry you got taken by the people at CMM. Perhaps you can request a refund, I certainly would.