Adobe Creative Cloud downaloded without my permission.

Same issue here, I don'tlike when softwares install themself without a permission. It's called spam or spyware.

The 'Creative Cloud' is not what you think. It's not only a platform for launching and managing 20 or 40 Adobe services you don't care about and to which you don't want to subscribe. As such it is free and does not imply any subscription. It does not take significant disk space and does not really slow down your work. To be clear, if you don't like both words, simply ignore them and work like before.

https://helpx.adobe.com/creative-cloud/help/benefits-creative-cloud-free-membership.html

What is new with PSE2021 (already used by thousands of users since nearly one year)?

It is part of the installation files for the PSE2021 package, at least for some users. It looks like it's a bit experimental and does not get many comments and help from Adobe, except that it offers a free small Cloud space giving new opportunities for PSE users to share their files, especially to share files with friends or with other Adobe Apps you may have. For instance, you can have the Bridge management software for free, which is a different system than the organizer and which gives you more power for managing metadata. You don't need to have a Cloud app like OneDrive or Dropbox to send a link to a big batch of new files to share.

As such, it's a chunk in the many files PSE installs in many locations of your System, and you don't have to give your permission for each of those different chunks.

As I see it, this is an experimental step, and we'll have to see what comes out of this in future versions.