How can I connect an external optical drive to a MacBook Pro 16" via USB-C?

Yes, you can connect external optical drives to a 16" MacBook Pro via USB-C.

In some cases, you might need to go between USB-A and USB-C – e.g., by using an Apple USB-C to USB adapter, or, if the drive has a detachable cable, by ordering a cable that goes directly from USB-C to whatever type of USB socket there is on the drive.

If we are talking about a portable drive, some drives like to suck down so much power that they want you to hook them up to TWO of your USB ports.

external optical drives that use only Bus power are difficult to get working properly, because they tend to need ALL of the available Bus Power to operate.

you can use System Information display to look at power required and available:

As far as things showing up in the Finder:

• Go into Finder > Settings… and make sure that you have "CDs, DVDs, and iPods" checked off in the General tab and "CDs, DVDs, and iOS Devices" checked off in the Sidebar tab.
• Note that empty drives will not show up on the Desktop or in the sidebars of Finder windows. When you insert a disc that has data on it, that disc will show in those places (if Finder Settings say to display discs there).