Big fan of the anime, haven't read the source material though so no clue whats expected to come. I personally thought season 3 was a bit slower paced than the first two seasons, or maybe it was just less Iruma focused, so hoping season 4 will be on par with the first two seasons in that regard.
As for when it'll come out I'm thinking Spring season 2024. Since each season has been roughly 6 seasons a part. 1st Fall 2019, 2nd Spring 2021, 3rd Fall 2022, thus Spring 2024 hopefully.