Has Apple discontinued Thunderbolt on Mac Pro?

No.

Mac Pro - Technical Specifications - Apple

Thunderbolt 3, 4, and 5 are all very important data AND display interfaces going forward. They all use the USB-C connector, additionally marked with the Thunderbolt symbol (a lightning bolt with a small arrowhead at the bottom).

if you own a Mac Pro 2013 model (the short dark cylinder) it features only ThunderBolt-2 ports, which have limited usefulness today. That model uses the Mini DisplayPort connector for its ThunderBolt-2 ports.

No, but they have discontinued support for Firewire which has become a topic of discussion on tech blogs.

Perhaps you are thinking about Firewire?

According to the specs for that Mac Pro, you should have the ability to connect three 5k displays or six Thunderbolt displays.

Mac Pro (Late 2013 - Technical Specs - Apple Support

What are the brands and the models of the three displays you are trying to connect?

if you look closely at the diagram I posted previously, the HDMI port shares Thunderbolt Bus 0 -- the bottom two ThunderBolt ports.

Be sure you have distributed your displays across as many Thunderbolt Busses as possible.

if you are converting any interfaces to HDMI or DVI, that presents a Power problem, and you will have to use at least one ACTIVE, powered, adapter (slightly more expensive).

JCPMonteiro wrote:

I can use 3 monitor from thunderbolt not work. Is possible 2 and work. Any configuration to use 3 monitors ?

what model-year MacPro 42 lb silver tower or dark cylinder?

or what model-year MacBook Pro notebook computer and what built-in display size?

Apple menu > About this Mac

Please don't include your serial number, it attracts vermin.

I can use 3 monitor from thunderbolt not work. Is possible 2 and work. Any configuration to use 3 monitors ?

The model is Mac Pro 2013 - Cylinder. Configure: 12 Cores CPU - 2x D300 and 64GB ram

I try connect:

2X Thunderbolt and 1xHDMI port and work 2 monitor. not 3.