FreeFileSync Forum

Go to www.speedtest.net to check your theoretical upload speed. If it is 2.5 MB/s, then no tool will help you.
In Generell with file sync, your overall speed is lower when you have many small files, because you have more overhead in opening/closing of files.
The advantage of Beyond Compare over ...

Do you really need assistance on how to google "Beyond Compare"?

I gave up looking and waiting for a solution and moved to beyond compare. Pro Edition can sync to Onedrive. It's not free but does the job very well.

How did you configure OneDrive?
I thought that there is no SFTP for onedrive available?