This seems confusing, but it should be fine. I created a new Debian 10 server and logged in as root. It’s an isolated network, so everything works just for testing. I have the main 500GB drive, plus a 1TB and a 2TB drive for backups and images. I made the directory structure with mkdir and mounted media/images. The output from lsblk shows all partitions correctly. When checking with fdisk, it lists sizes and sectors properly. The swap space is also present. Everything looks set up as expected.
Recall that dev and media are located in /, and mount /dev/sdc1 /media/images
Verify your commands correctly. The path needs the full first slash. Using `mount /dev/sdc1 media/images` should function, but it’s better to type complete paths or enable autocomplete to confirm existence.