After the 2019 World Cup, Sri Lanka has played three ODI series and Test series and five T20I series. From the three ODI series, they won two against Bangladesh and West Indies. Further, from three Test series they won only one against Zimbabwe and tied the series 1-1 against New Zealand. However, from the five T20I series they won only one against Pakistan. Therefore, there is a lot to improve in the longest and the shortest format of cricket.
ODIs
In the 2019 World Cup, they finished sixth on the points table. The issue was their middle-order batting. However, since Angelo Mathews has returned this issue has been solved. The win against England in the World Cup, Mathews played an important role with his bat. Afterwards, in the series against Bangladesh, he was the player of the series due to his batting performance. Therefore, it is important for Sri Lanka to have someone like Mathews in their middle-order who can guide the young batsmen from the other end.
Further, this has reduced the pressure of their top-order batsmen. Moreover, it makes a good platform for finishers like Thisara Perera and Wanindu Hasaranga. Further, in their bowling, they somewhere lack experience. Therefore, it was important for Mathews to start bowling again. Further, this proved to be fruitful for Sri Lanka, when in the final ODI against West Indies, Mathews picked crucial four wickets and Sri Lanka won that tight match. Therefore, the point here is Sri Lanka has to still work on their bowling.
Test Cricket

In Tests, their performance in the last one year was hot and cold. If we see the summarized scorecards, one name which frequently repeats there is Lasith Embuldeniya. In the three Test series, he has picked 32% of wickets for Sri Lanka. Moreover, when he failed to pick the wickets, the opposition made big runs and the game used to move away from their hands afterwards. The story it tells is Sri Lankan bowling is very much dependent on him or other spinners. Therefore, moving forward this will be an area where they will have to work and be ready with a proper plan B.