Hi,
Just wanted to share that I managed to install successfully Ubuntu Touch on my Xperia X which was running SFOS before.
Here are the steps performed :
- flash using Emma tool "F5121 34.4.A.2.107 Customized_FR 1302-3046 R4E User-Live COM" (Android 8.0) : kernel was not upgraded and mobile wanted to shutdown all the time
- flash in fastboot mode twrp-3.3.1-0-suzu.img for recovery
- boot in recovery mode and from twrp : wipe Cache, System and Data
- reboot (oops can't boot, stalled with Sony image)
- boot in fastboot mode and run UBports Installer 0.4.18-beta
- select channel 16.04/community/fredldotme/devel, Wipe Userdata and Bootstrap
- let the installation process run and discard any display on mobile
- and it worked !
OK. I have to admit I stressed a lot while performing the different steps 
.
Now, I am discovering UT on Xperia X and I am impressed by the work done on this phone 
!
For the moment, I have noticed following issues :
- front and back camera zoom are not working
- back camera autofocus is not working
Congrats @fredldotme !