Currently varbinary type columns are not supported in Flow for SQL Server and Azure SQL Database.
This is essential to be able to properly work with documents stored in SQL Server.
I have managed to upload from Flow to SQL Binary. Go and check out these two videos and let me know if this works for you.
Introduction - https://youtu.be/wJj0E1C4z0c
Using Variables in file upload - https://youtu.be/sgAx3aaRL8E
SQL Binary - https://youtu.be/hif0VfOhhMA
There are some other videos in the series but that is for OneDrive and SharePoint.