do you think vnc could make a conflict with uart?
No! I canât see why VNC would have any impact on UART.
I donât know too 
still searching what s the problem!! I am reformatting the sd know and wil all restart from scratch!
Try connecting RPi pin 8 to pin 10 and see whether you can see data sent, e.g. start a comms app like miniterm and check you see what you type then remove the link and check you donât see it. This will prove the UART is not damaged. You may want to do this with a basic Raspbian install, e.g. Raspbian Lite.
Similarly you could wire the RPi side of the MIDI interface to a 5 pin DIN and connect to a sound module to check the MIDI is being passed through.
ITâs all set up around the TTY port and thatâs really what you want to know is functioning. Checking that can be a little bit involved. In the very eary days and when we moved from Pi2 to Pi3 I seem to remember we eeded to change the value of the basic MIDI clock value that set up the TTY port, but that really is ancient history.
A âsimpleâ GPIO sketch using a Raspian SSD would at least allow you to see if you can get the Opto-Isolator actually controlling the GPIO pin that MIDI comes in over.
As @riban says you probably want to check the opto-isolator actually does the sorts of things itâs meant to.
I already relied this too, I think my raspberry has a problem
oh damn after reinstalling now cdmi doesnât work too, I ll stop trying Zynthian I believe, I already spent 2 days on it and all is too cinfusing for me! thanks for your help btw