Why is UDP so slow?

I have Khadas vim3.
I’m checking the speed using iperf3. A normal connection to a computer has a speed of almost gigabit, but when transmitting over udp, the speed becomes about 15-20 megabits per second. Maybe you need to enable some option to increase the speed?

P.S. I connected a laptop to the receiving device and the speed lan gigabit with a normal connection and over udp.