A wall without a hole
Update: Apple has released macOS 11.2 on February 1, 2021, removing the controversial ContentFilterExclusionList.
It seems that Apple is willing to admit mistakes. The unfortunate hole in the wall that raised a lot of privacy and security concerns in the Mac community appears to get closed in the upcoming version 11.2 of macOS Big Sur, allowing third-party firewalls like Little Snitch to reliably monitor and filter any network traffic again.
Thanks Apple for listening!