This is intended to be a resource for changes in 9th that can be easily referenced. Most of these are YouTube just because it's been things I can listen to while working.
Full Rules Leak - Google Drive from Lyraeus
Summaries from Other People
11 Changes to the Movement Phase - MiniWarGaming YouTube
6 Changes to the Shooting Phase - MiniWarGaming YouTube
Top Rule Changes in 9th from Playtesters - Tabletop Titans YouTube
Unit Coherency - Auspex Tactics YouTube
PDFs for Secondary Objectives and Mission Reference - Microsoft Drive via Reddit
Actions - Goonhammer
Big Core Changes including Coherency, Engagement Range, Modifiers, the Command Phase - Goonhammer
Movement including Turrets and Stay Stationary - Goonhammer
Command Re-roll and its effect on 2d6 rolls - Goonhammer
Psychic and Shooting changes including 'Look Out, Sir' - Goonhammer
Combat, Charge, Engagement Range, Flying while Charging - Goonhammer
Morale, Coherency, New Universal Strategems - Goonhammer
Terrain - Goonhammer
Faction Specific
Imperial Guard - Tabletop Titans
Harlequins - Tabletop Titans
Craftworlds - Tabletop Titans
AdMech - Tabletop Titans
Custodes - Tabletop Titans
Orks - Tabletop Titans
Death Guard - Tabletop Titans
Space Marines - Tabletop Titans
Tau - Tabletop Titans
Ideally discussion should be kept to the big 9th thread that already exists, but please suggest more resources! I will update this thread with suggestions, and additional links that I come across.