Website recovery not successful

I’m am using Updraft for some years now, but since some time I’ve got the problem, that restoring is failing.
If I try to restore a backup of my website, I am prompted from the system to delete old folders: “Existing unremoved folders from a previous restore exist (please use the “Delete old folders” button to delete them before trying again)”.
After having done this, the backup is running, but the website could not be restored successfully:
“Restore failed, error message: Couldn’t get rid of old files. You should check the ownership and permissions of the files in your WordPress installation.”
It looks like Updraft can’t delete the folders.
How can I solve the error?
Would it bring a solution, if I manually deleted the specified folders using FTP access.
Or do I have a general problem with the Updraft plugin?

The page I need help with: [log in to see the link]