Thanks for the feedback. I’m working on some changes for the update instructions, which still need some work but are forthcoming. As for you issues at the moment:
According to your report about the window is closing very quickly, your update has not succeeded. It should take a few seconds at least for the script to complete when it has executed properly.
For your question about the SYSBOOT button, you only need to hold it for a brief extra moment after releasing the RESET button. Holding SYSBOOT for one extra second is fine. Once you’ve done that, you should see “STM32 BOOTLOADER” in the list in Zidag if the USB connection is functioning.
Since “STM32 BOOTLOADER” is not showing in Zidag, I think you probably have an improperly functioning connection via the micro USB cable. I sometimes have to fiddle with my USB cable connection at both ends to make the connection work. You might also be using a power-only micro USB, which will never work (I had such an experience recently). So, I also suggest trying another micro USB cable. Unfortunately, it’s hard to know for sure when a cable is power-only because it often not marked in any way on the cable. If you are able, I would try one that you have used for, say, transferring data to an Android phone or other device connectivity so you can be sure it’s functional for data.