Teensy4.1 MAX baud rate

[MO_YA_NE]

Hi！
I have been teensydiuno for the third day.
I want to communicate with other MPUs at high speed using RS485 communication.
I set the teensy 4.1 hardware serial to 6Mbps, but higher values ​​didn't work.
Is there any way to get higher speeds?

void setup() {
//  Serial1.begin(3000000);     //3M OK
    Serial1.begin(6000000);     //6M OK
//  Serial1.begin(12000000);    //equal to 6M

}

void loop() {
  Serial1.write(0x55);
  delay(1000);
}