I had the same issue on Matlab R2023a Update 5 with a Nano 33 IOT, Windows 10
In my case Host COM port AND Bootloader COM port were different numbers.
I did not find the Bootloader COM port number in the Device Manager in the beginning (only the Host COM port). The solution is to press the reset-button of the Nano twice and observe the dropdown menu Ports (COM & LPT) in the Device Manager.
Then it was working.
HTH