343 Industries has just released Halo 3 and Halo 3 ODST PC screenshots. These screenshots are directly from the game, which is also known as game engine footage. Therefore, the final result you will play on PC will be the same as the ones you are seeing right now.
On the other hand, the quality might get better in the final game. Since we see the work in progress elements of the game, some differences might be visible. After Halo: Combat Evolved Anniversary, these two titles will be added to the Halo: The Master Chief Collection PC.
— Halo (@Halo) March 3, 2020
Therefore, Halo 5: Guardians will be the only remaining game of the series which is not on PC. This is (possibly) mainly because to direct the players to the Xbox platform if they want to enjoy the latest Halo experience.
Right now, it is not clear if we will ever see the latest title on PC or not. If you would like to take a look at the screenshots of Halo 3 and Halo 3 ODST on PC, check the gallery above. We will let you know if new information surfaces.