Deleting backups

Hi, I am trying to delete not used backup files. The server is a Rp4. I have disconnected the external HDD where the backups for sent. Connected to a windows machine, but i am not able to delete the folder or better to say it takes forever. So how do i get rid of those files?
thanks

What partition type is the storage?

Is there too many files in there which could cause long time to read?

Your HDD might be having bad sector which is reason for the hiccups.

Your might be connected to usb2 in your PC which is slow

The external HDD connected has ntfs using SATA2 to connect. However i went back to the linux machine and using nohup in a few hours everything has been deleted. But my question is why are there so many files, some thousand?