what is the name of the biggest ipad that artists use? I can't find it here.

I don't really understand the question but the biggest size iPad is the 12.9 inch iPad Pro.

No apple device has 14.5 inch screen

The largest model of iPad is the 12.9”. The current model is the 2020 iPad Pro 12.9”.

There is no Apple tablet or Apple device which is 14.5inch screen.

Maybe it wasn't an apple and it was another brand

When measuring the screen, you should only measure diagonally across the active/visible screen area. Do not include the screen bezels that surround the visible area of the screen.

If its an iPad you should be able to open the Settings App and navigate to General->About->Model. Tell us what it says there.

Also, a picture of what you actually have would be useful.

As has been mentioned there is no Apple device at this time that has a 14.5" inch screen measured diagonally.