No, that’s not necessary and also not recommended (because this also removes your registration information).
However, your installed Little Snitch 4 version will then no longer be loaded on macOS Big Sur and must be upgraded to Little Snitch 5.
→ Download Little Snitch 5 for macOS Big Sur
When you upgrade to Little Snitch 5, the existing, outdated installation will be automatically removed (this requires a restart of the computer for one last time).
Your existing rules and settings from Little Snitch 4 will be preserved.