In the meantime I thank you for answering me so quickly; however I don't think that the problem is generated by the outdated antivirus, after all the problem appears from ccleaner 5.65.7632 version and persists in the following versions, so the various antivirus manufacturers had plenty of time to update...
My security suite is the Comodo Internet Security Premium v.12.0.6818, while the operating system is win10x64 home, first the 1909 version, now in 2004 the same problem continues to occur.
Now, regarding the Comodo, if the processes are signed, there is no need to create additional rules, it seems to me that ccleaner (if I'm not wrong) is signed, consequently in my a.v. the process in question must work (!) correctly, in any case, I will make additional tests with the Comodo, but honestly I think it is a waste of time...
I think it is easier (but this is just my hypothesis) that it is a virus that prevents ccleaner64.exe from working correctly/loading, and I repeat this to be further as clear as possible, the only version of ccleaner that works without any problem is v.5.64.0.7613, while all the following ones, reaching the current one, the last one (I think) that is v.5.70.7909 crash and there is no way to start them!
Hello and thanks again for your patience.