Assuming not much has changed I can see a few differences:

• The UNSC (known as the Union of Socialist Star Systems or USSS) would have the military either disbanded or defunded heavily, either way the covenant war would be force a rearmament. I imagine the war would be as disastrous as the Gold Timeline albeit a little less
• The Sangheili and other species would probably be more hostile to humanity after the war due to communism.
• Any captured Covenant technology can be reverse engineered faster due it not being gatekeeped by greedy private corpos and civilians being allowed to test with de-tracked materiel (de-tracked because Rubble).
• The biggest difference I can see is the tension between Earth and Outer Colonies being less prevalent due to democratic centralization.

That’s all I can see. Idk what would be of the Halo Array or The Flood or Banished, whatever.