Table size in Azure SQL Managed Instance vs On Premise SQL Server
The Accelerated Database Recovery (ADR) feature introduced as part of SQL Server 2019 is enabled automatically on SQL Server Managed Instances.

Part of the way this feature is implemented is to include a 14 byte row versioning tag with each row.

14 bytes per row * 10,000,000 rows = 140,000,000 bytes = 133.5 MB of extra data to support ADR.

This explains the entirety of the difference in the approximate numbers provided (336 MB - 198 MB = 138 MB).

You should see the size of the SQL Server 2019 database match the Managed Instance size if you enable ADR prior to loading the 10,000,000 rows:

ALTER DATABASE [YourDatabaseName] 
SET ACCELERATED_DATABASE_RECOVERY = ON;