Interesting and not so nice.
https://www.ghacks.net/2019/09/25/microsoft-blocks-official-ccleaner-domain-on-its-answers-site/
Interestingly enough I have a test Win10 system here with CCleaner installed, it appears Microsoft might be pushing the blocking further than their websites as Controlled Folder Access in Defenders Ransomware blocked two CCleaner actions a couple of days ago which has never happened before.
All backend services of CCleaner are/were disabled including update checks and the program was not even open when the block actions were performed, to much suspicious behaviour from CCleaner and more recently reported damaged systems plus the bundled installer junk are some of the reasons consumers and Microsoft have had enough.
Avast took a once great little tool and ruined it

thankfully I've removed CCleaner off all systems I still maintain these days and replaced with a more trustworthy and safer software Cleanmgr+
https://www.getclone.app/ms-apps/cleanmgrplus