What you are trying to achieve:
Connect Pixhawk 6x to Matlab/Simulink for custom controller deployment.
Platform
Windows 11/ Matlab R 2023 b / Hexacopter / px4_fmu-v6x_multicopter build
Github issue already created
Link
Com port issue with Version 1.12.3[Bug] · Issue #22780 · PX4/PX4-Autopilot · GitHub.
Will try to wrap it under 5 mins