Starting with macOS 10.15.4 the above “Legacy System Extension” message is shown when Little Snitch is installed.
Is there an update of Little Snitch that’s compatible with macOS 11 Big Sur?
Yes. The latest version 5 of Little Snitch (currently in beta) is fully compatible with macOS 11 Big Sur. → Learn more…
Will I get the update for free?
If you have purchased a Little Snitch license after November 1, 2019, this license can also be used to register Little Snitch 5. If you purchased Little Snitch 4 before that date, you can get the upgrade at a reduced price.
Will Little Snitch 4 run on macOS 11 Big Sur?
Little Snitch 4 will not be loaded on macOS 11 Big Sur by default, but there will be an option to manually override this system default.