Solidworks 2020 introduces a new mode known as the “Detailing mode” that allows for large drawing files to be open faster for minor edits and design reviews. The model data is not loaded but the drawing views remain intact, so there is no loss of detail in your drawings.
The detailing mode allows closed drawings to open faster, however, in some cases this will cause issues in the Save operation of the drawings, as additional detailing mode data is required to be saved.
To improve your save times, you will need to disable this setting in your System Options, which has been made available from the SW 2020 Sp4.0 version. This only affects the 2020 and 2021 installations as the bug has been resolved in the 2022 version.
Go to System Options > Drawings > Performance
Uncheck the option for “”Include detailing mode data when saving”.
Close SOLIDWORKS and try the save operation again. This should result in a faster save time.