Go to Menu > Tools > Accounts and make sure that diagnostic logs are not enabled.
Also, check in Menu > Tools > Settings > Advanced, that none of the logs are enabled. You can also clear the logs there and see if that makes a difference.
With the change of version, there were most likely some changes made to the database structure. That has always been there in the past, but I can’t say that I have noticed a significant change in the overall database size as a result. Looking back at my last year of backups, the size increases daily as more data is added, but that is to be expected.
The right-side screenshots are taken with eM Client running. How do the sizes compare when it is not running?
Sometimes when there are some errors, extra files are created. With eM Client closed, you can manually run C:\Program Files (x86)\eM Client\DbRepair.exe and see if that reduces the overall size.
Some additional files will always be created with SQLite databases when they are being used. WAL files (write ahead logs) cache the data and append changes to it when the database is open while preserving the original data. If something goes wrong, those files can be used by DbRepair to reconstruct the data. I always understood that they were deleted after the database was closed, but maybe that is not the case. Maybe someone with SQLIte experience can comment on that.
When DbRepair is run, it should delete them if no errors are found, but they will always be recreated as soon as you open the database again.
These files are not included in the backups made with eM Client’s internal backup.