Since first phase of the Shingeki no kyojin - The Final season ended... I want to read the manga for it ahead, I can't wait for a whole year. Where should I start?
I did a little research and found out that the last episode of the Final season (season 4) of Attack on titan ends on chapter 116 of the manga. the next season (Attack on titan - The Final Season Pt.2) will probably start from chapter 117, so start reading from there.
But, for more convenience and understanding of the proper situation and the story, read chapters 115 and 116 as well, because there are some things, and certain scenes that they didn't include in the final episode, but can be seen in the manga.