Did the anime cover all the manga up to Season 4 of Shingeki no Kyojn? I would like to read the manga after Season 3 Part 2 of the anime Shingeki no Kyojn. But I would like to ask if the anime covered the manga chapters before it?

Clarification:
MAIN QUESTION. Did the Anime include all that there is in the manga (at least the chapters up until the last part of Season 3 Part 2 of the anime)?

If not, what are the manga chapters not included so that I could read them before proceeding?
No, it does not. The anime is behind the manga by more than 30 chapters. 

The last episode of the latest Attack on Titan season adapted Chapter 90 of the manga so Season 4 would, presumably, start from Chapter 91.

It should also be worth noting that Season 4 is the last season for the anime series, given that the manga is already on its final arc.