I have the same problem. After the update to v5.65, ccleaner could not be opened anymore. I also tried the Portable version.
Since I had to reinstall my PC anyway because of problems, I didn't care.
After the reinstallation, however, the same problem again.
After reading here that it might have something to do with the virus scanner, I tried it right away. If Trend Micro is completely closed, ccleaner v 5.65 can be opened, otherwise not (also Portable!). ccleaner v5.64 works without any problems!
Win10 pro 10.0.18363
Trend Micro Maximum Security v16.0
OK, who can read is clearly in advantage...
After I have included ccleaner in the whitelist of the TMMS it works again.
Funnily enough, I've never raised problems with ccleaner and TrendMicro and I've been using both forever...