I have tried all the suggested fixes and even taken the computer to a professional that tried many fixes. He told me the program was not compatible until a software fix was published by ccleaner.
About 20 hours invested so far with no results.
The compatibility chart says the latest ccleaner is designed for Win 8
Which version of CCleaner are you trying to install? I assume the latest v5.74.
And which antivirus?
We often see issues when a new version of CCleaner is released with certain AVs stopping them from installing.
It can take a few days, or in some cases a week or so, before the Antivirus updates to recognise the new CCleaner version.
Certain Antiviruses are more prone to this (slower to update) than the majority.
Plus some antiviruses will say that they are up to date when in fact they are not.
(For instance Trend Micro 2019 will say that it's up to date, but the latest is Trend Micro 2020 which you sometimes have to get manually from their website).
You could try going to your AV makers website and check what the latest version is there.
Had you successfully installed a previous version of CCleaner on this computer prior to updating to Windows 20H2?
We have seen users have problems with a variety of software installation after some prior Windows updates when Windows "helpfully" resets your Windows store settings and wants to insist that you download something from the Windows store instead. Are you getting a Windows Store pop-up when you try to run the installer? If it is some other error message that is popping up, could you provide us with a copy please?
As Dave has asked you should check that, I've had that happen myself following a Windows update.
It's in Settings>Apps>Choose where to get apps.
If the update has set it to 'The Windows Store only' then it usually (but not always) prevents downloading of anything at all that is not from the Windows store.
If that isn't the problem then our next 'go to' trick is to try downloading the 'Slim' installer from here (it's the third one down) and once it's downloaded double click it to install CCleaner:
It installs exactly the same version of CCleaner but the Slim installer can sometimes work when the Standard installer is being blocked for some reason.
same problem here with Windows 10 Pro 20H2 (19042.662). The CCleaner installer does not install anything, the slim installer of the latest version 5.74.8198 does. MS Store was not the issue and only AV software is Defender.
Next problem after installation which went without errors: CCleaner does not start.
Nothing in the task manager, no errors at all. Double click does nothing. Windows sees the program as "incompatible". Maybe it is.
PS: I have used CCleaner for years and very regular.