I was able to install Ubuntu Touch on Aquaris M10 HD with pre-installed Android 8.1.0. I am not experienced in flashing mobile devices therefore some things shown in the video were unclear for me but still very useful. I don't know what was important so I'm posting these steps combined from the video and official instructions that were lucky for me. If there is something wrong with it, please, correct me. Hope that it will help other unexperienced users in the future.
Start pre-installed Android 8.1.0 on the tablet (hold "Power" button) and enable developer mode and USB debugging there.
Power off the device by holding "Power" button.
Start the tablet by holding "Power" button and "Volume Up" button to select device's boot mode.
Choose "Fastboot mode" by "Volume Up" button and then press "Volume Down".
Device doesn't reboot automatically. Power off the device by holding "Power" button for a few seconds and then start it again by "Power" + "Volume Up" buttons and select "Recovery Mode".
In recovery menu select "Reboot to bootloader" item using "Volume Up"/"Volume Down" buttons and press "Power" button. => FASTBOOT mode... text will be shown at the left bottom corner of the blank screen.
I guess it's time to flash the firmware, but it was unclear from the video whether I should power off the device or not. So according to these instructions I decided to power off the device (hold "Power" button for a few seconds).
Download recent version of Smartphone Flash Tool and extract it's files from the archive. I used version 5.1916 for Linux 64-bit. To be exact, I'm on Kubuntu 18.04.1.
Install missing library for SP Flash Tool:
$ wget -q -O /tmp/libpng12.deb http://mirrors.kernel.org/ubuntu/pool/main/libp/libpng/libpng12-0_1.2.54-1ubuntu1_amd64.deb \
&& sudo dpkg -i /tmp/libpng12.deb \
&& rm /tmp/libpng12.deb
Go to directory with SP Flash Tool and make it executable:
$ cd ~/Downloads/ubports/SP_Flash_Tool-5.1916_Linux
$ chmod +x ./flash_tool.sh
Start SP Flash Tool with root privileges:
$ sudo ./flash_tool.sh
Download old Canonical UT image called cooler for M10 HD, unpack it and select Android_scatter.txt file from there in SP Flash Tool ("Download" tab => "Scatter-loading File").
Choose "Firmware Upgrade" from dropdown list.
Press "Download" button at the top left corner of "Download" tab.
Connect powered-off tablet to USB 2.0 port of the computer. "Magic happens" — old UT image will be downloaded into device and installed.
I saw BQ logo with "Powered by Ubuntu" label at the end but unfortunatelly further UT loading was stuck. Nothing happened for a long time.
Download recent version of UBports Installer. It was deb of version 0.4.5-beta for me.
Start UBports with root privileges:
$ sudo ubports-installer
and follow it's instructions.
When I ran "Reboot to bootloader" and saw => FASTBOOT mode like it was in 6, I didn't power off the tablet before connecting to computer. Everything was fine, I got rotating Ubuntu logo on the screen first, and working fresh Ubuntu Touch image three minutes later.
