A backup of a Mac fails with:
Error code: 65521
Message: Resource deadlock avoided
The folder /Users/[username]Library/CloudStorage/<XXXXXX> is the folder for iCloud files on Mac. These files are stored on the cloud rather than on the local machine.
Acronis Cyber Protect Cloud: This issue has been fixed in C21.12, please update to the latest build,
Acronis Cyber Protect 15: this issue has been fixed in Acronis Cyber Protect 15 Update 4 (Build 29240). Please update to the latest build.
If this path is specified explicitly there still will be a warning because the files are really in the Cloud.
Workaround for earlier builds: go to 'File filters' option > 'Do not back up files matching the following criteria' and add the following 2 lines: