Thanks Ciber Sheep.
I managed to install the 3.0.4 Freezerhead image disabled automatic update in developer options, did not allow any web wifi connection to prevent any update.
BUT I tried the installer twice, and could not install UT on the tablet.
First the installer recognizes the BQ 10 M HD and tells me it is not supported, so I selected it manually.
The device is unlocked, and it proceeds with the install.
Then some warning says something went wrong, so i click on the ignore button, and it keeps on going.
after a long while, it says successful install, I wait 10 minutes, reboot and NO UT still on Android.
Actually the installer never worked before on this tablet unlike on my Pixel 3 a XL.
I read somewhere that it needs a larger partition or something...
I kept on trying the installer from time to time hoping the updates would have fixed this issue.
I bought this tablet in 2018 so I could run UT on it.
It has been a long patience game.

Hi everyone !
I completely bricked my BQ M10 HD using Gparted to format the whole SSD memory.
I intended to create a new FAT 32 partition on the unused space, but Gparted did not show anything at all.
I only get a frozen splash display if the charging cable is connected.
I think the tablet is in its prime virgin OEM state before flashing any OS on it.
Can't go on boot loader mode or anything else.
It became unusable running on Oxygen custom ROM.
I don't have much hope of fixing it now, please tell me I'm wrong, and there is an easy fix for it.