@phandersson
Further experimental results. I just watched a tutorial video on how to root the phone (just in case), and it starts with early steps that are very similar to the ones I followed, so I tried those as well:
- enable dev mode + USB debug (already done, obviously)
- connect phone to PC
- type "adb devices" => device is listed:
$ adb devices -l
List of devices attached
dbXXXX device usb:1-1 product:jasmine model:Mi_A2 device:jasmine_sprout transport_id:2
- type "adb reboot bootloader" to reach fastboot: the phone does reboot and reaches the fastboot splash screen
- use fastboot to boot on TWRP image -- this time, the message was different (although it still doesn't work):
$ fastboot boot ./twrp-3.5.2_9-0-jasmine_sprout.img
Downloading 'boot.img'
FAILED (data write failure (Cannot send after transport endpoint shutdown))
Finished. Total time: 0.850s
And indeed, the fastboot environment appears to have crashed: the fastboot splash screen is gone, and the phone displays a short text message: "press any key to shutdown" (pressing power then reboots the phone).
As the message could hint at a data transmission problem, I tried the same procedure with the other USB-C cable, and this time the output for the last step was:
$ fastboot boot ./twrp-3.5.2_9-0-jasmine_sprout.img
Downloading 'boot.img'
FAILED (remote: unknown command)
Finished. Total time: 0.012s
So, similar to the behaviour described in my initial post above. But I'm a bit concerned by this lack of repeatability...