Enhance the "Block syncing of specific file types" to stop the ODFB Sync client from downloading blocked file types FROM the tenant to the client PC.
I have blocked MP4 files via the "Block syncing of specific file types" at https://admin.onedrive.com.
I put an MP4 file into the root of my OneDrive for Business folder on my local PC to send it to my O365 tenant.
The Sync client correctly blocks this and makes me remove the MP4 file from my local PC.
Open https://tenant-my.sharepoint.com and upload the MP4 file via the browser to the site.
Wait a few moments.
The MP4 file appears in my local harddrive's folder that contains my synced files and folders. This is inconsistent behavior that reduces our ability to control what is stored in OneDrive for Business by our users.