it's an M1 with 16 GB RAM I guess. You have at least a 256GB SSD internal Hard Drive.
The 4 TB Hard-Drive you're speaking about - you plug it in your Mac with a cable, right? Is the plug large and rectangular or smaller with rounded edges?
You can try to follow Apples suggestion on optimizing your storage:
Learn what to do if your Mac startup disk is almost full, or you don't have enough storage space to download, install, or copy.
support.apple.com
Do this "Choose Apple menu > System Settings, click General in the sidebar, then click Storage on the right" and tell us how much space is available and how much is used. It should look like this:
View attachment 2183206So