I2C initialisation problem with MLX90614

Yay, it works with I2C3.setup( { scl: A8, sda: B4 } ); on the pico. Thank you!!

I've checked the other I2C-pins too:

1. I2C1.setup( { scl: B6, sda: B7 } ); // not working
   2. I2C1.setup( { scl: B8, sda: B9 } ); // not working
   3. I2C2.setup( { scl: B10, sda: B3 } ); // working
   4. I2C3.setup( { scl: A8, sda: B4 } ); // working
   
   But USB is always connected. Is there really no difference between I2C1 and the I2C2 or I2C3?