The MS store has updates every Saturday the top paid list which is the best selling games for the past week. In the US and in the UK (Xbox biggest markets) Sea of Thieves has outsold Far Cry 5 this past week.
US Store https://www.microsoft.com/en-us/store/top-paid/games/xbox?icid=CNavXboxGamesDownload
1. Sea of Thieves
2. A Way Out
3. PUBG
4. Far Cry 5
5. Fortnite
UK Store https://www.microsoft.com/en-gb/store/top-paid/games/xbox
1. A Way Out
2. PUBG
3. Sea of Thieves
4. Fortnite
5. Titanfall 2(on sale for $6)
6. Far Cry 5
Pretty Impressive that SoT is outselling a big AAA that just released.