When I plug my CD player into a USB port I dont see it on my screen, Why

Macs will not show the drive unless there is a disc inside it can read correctly.

Also, make sure that CD/DVD drives are set to be displayed on the desktop and in Finder, in the Finder Settings in the General and SideBar tabs

Bilabong wrote:

My iMac doesn't appear to recognize my CD/DVD drive. When I plug it into the USB port its icon is not visible on my home screen. The same USB port recognizes a flash drive alright. I can hear my CD drive power up when it's plugged in but no display visible on my screen. Why?

Be sure all these checkboxes are checked:

The empty drive will not appear on the desktop.

You must insert a CD or DVD. These will appear on the desktop.

If they do not, check Finder > Settings > General and check mark the box to show "CDs, DVDs and iPods".

More likely, the CD that's inside cannot be read by the Mac.

What is this CD of? Music CD? Data CD? Photo CD? Application CD?

If he drive powers on, and you hear it spin, and has a blinking light, it meas its working.

Bilabong wrote:

My iMac doesn't appear to recognize my CD/DVD drive. When I plug it into the USB port its icon is not visible on my home screen. The same USB port recognizes a flash drive alright. I can hear my CD drive power up when it's plugged in but no display visible on my screen. Why?

The Finder shows mounted volumes.

A volume is something that has a filesystem, and can store data. Could be a formatted hard drive, SSD, USB flash drive, memory card, partition, CD/DVD data disc, or mounted disk image file (.DMG).

An empty CD/DVD drive has no filesystem and no stored data. It's just a device. If you insert a blank recordable / rewritable CD or DVD, there's still going to be no filesystem and no volume until you burn one onto the CD or DVD.

Note that Apple dropped all support for the HFS (no "+") filesystem in Catalina.

This has had a very unfortunate effect on the ability to read CDs burned on old Macs. If a CD-R was burned in Mac format, with HFS as the filesystem, modern versions of macOS will refuse to read the disc. Even if it was burned in hybrid format, and modern versions of macOS could theoretically read the filesystem meant for a Windows PC, the mere presence of a HFS filesystem will reportedly cause modern versions of macOS to reject the disc.

Try a different CD to see if the problem is the CD you have been using, or if it's the drive.