It’s simply no longer possible to read and write everywhere, as lots of directories has been blocked completely. That is why CleanApp is discontinued and not sold any longer.
While CleanApp lost functionality with every macOS update, Big Sur unfortunately marks the end of this app.
There is no replacement – macOS’ own clean up features (“About this Mac”/Storage/Manage) might come in handy, though.
We recommend to remove CleanApp from your Mac. In case you were using CleanApp’s logging feature, please remove its database manually. It is located here: