I am just getting started with the Xiao and can confirm this behavior: I have two Xiao from 2020 and they have same UUID.
I am using MacOS 10.4.6 and latest versions of Arduino IDE and Xiao. When I upload a sketch, I get the “disk not ejected properly” message and the Xiao is flashed properly with no issue but the message is annoying.
Additionally, even when I eject the Xiao “properly” in bootloader mode, after unplugging the Xiao from the USB-C cable, the “disk not ejected properly” message pops up too.
Thank you for sharing this workaround to alleviate this annoyance.