htc u12+ flashing twrp, stuck booting
My reply from the XDA support thread was already posted here, however I will formally reply now that if you're seeing &quot;flash images success (1/1)&quot;, then you're in Download mode. In order for the &quot;fastboot boot&quot; command to work, you have to be in Bootloader. There is an option to &quot;reboot to bootloader&quot; from the main Download mode screen. Choose that option, and then you will be in the correct mode to use the &quot;fastboot boot&quot; command.
You mentioned U11, however the difference with that device is that it has a recovery partition (U12+ does not), and thus the install method for it is to flash the image, not boot it. If you wanted to fastboot boot a recovery image on U11, you likewise would need to be in Bootloader mode.