We do not have a download file for the latest version (10.9.5903), but you can try downloading it from the developer's site
Download version 10.4.4395 from Software Informer
Scanned by 76 antivirus programs on Oct 15, 2023.
The file is clean, see the report.
Version: 10.4.4395 (x86/x64)
Date update: Jan 30, 2018
File name: synthesia-10.4-installer.exe
Size: 3.7 MB