Will it damage my iPhone 12 Pro if I use my old iPhone X charger? Verizon told me it would.

That will not damage it. In fact, Apple encourages it. See the following from Buy iPhone 12 Pro and iPhone 12 Pro Max - Apple

As part of our efforts to reach our environmental goals, iPhone 12 Pro and iPhone 12 Pro Max do not include a power adapter or EarPods. Included in the box is a USB‑C to Lightning cable that supports fast charging and is compatible with USB‑C power adapters and computer ports.

We encourage you to re‑use your current USB‑A to Lightning cables, power adapters, and headphones which are compatible with these iPhone models. But if you need any new Apple power adapters or headphones, they are available for purchase.

I have tried to use the old iphone 10xr cable with my new iphone 12 pro and IT DOES NOT WORK! i would like to be able to hook the new iphone 12 pro to my computer to transfer music and audiobooks from itunes, but when i plug the cable into the phone nothing happens, it worked fine in my old 10xr but not in the new 12 pro i am wondering what kind of BS Apple is pulling with this garbage??????????

None. As I mentioned in your other post of my my USB-A to Lightning cables works fine. Can you charge your iPhone with the cable?

i can charge the phone with the supplied cable but no other cables i own that worked in my old 10 xr phone work in the 12 pro phone.