The operation can’t be completed because the disk is full.

I have created a new blank disk image and opened it, I then tried to drag-and-drop my .pkg file inside it but I got a pop-up message saying "The operation can’t be completed because the disk is full.". I dont understand why this is happening because I have 148 GB available and the disk volume holds way more than the .pkg file itself.. I tried multiple things to fix it such as safe mode, adding way more room to the disk, using terminal but nothing really seems to work..

here's a screenshot of my storage and how much I have available and the notification I kept getting.

can someone please tell me why this is happening and how I could fix this? thank you