iCloud synchronization issues and Safari hangs after macOS Tahoe 26.0 update

I recently "upgraded" to Tahoe 26.0. All my data is stored on iCloud. But I am having major problems. Safari hangs so badly that I have had to switch to Chrome, and now files - although I can see them - act like they are just waiting to download for me to access. This is not a problem with my Macbook Pro, which I did not "upgrade". The one thing I may have done wrong was to run CleanMyMac in an effort to fix the Safari hang problem. I fear that App may have broken something.

[Re-Titled by Moderator]

Original Title: iCloud synchronization problem