Hello,
I tried the Installation more times. Now I have had luck. The Phone works.
This ist what I have done (Sorry for the bad English):
Flash Sony Xperia F5121
1.1) Unlock access to the cell phone
- Activate "USB debugging" and "bootloader access" on the mobile phone in Android (see Android on the Internet)
- Have the "Unlock code" displayed on the Sony side, stating the cell phone's IMAI (and write it down)
1.2) Install Android 8 - Install the "Fastboot" program on the PC sudo apt install fastboot
- put the mobile phone in bootloader mode (switch off the mobile phone; wait 15 seconds; hold the volume up key down; plug in the USB cable; if the LED lights up blue the connection is established)
- Check in the terminal whether the cell phone can be reached with "fastboot devices" (the device should be displayed)
- unlock the bootloader with fastboot oem unlock 0x[unlock code from Sony]
- remove the SD card first !! (if available)
- Install the flash tool from Sony under Windows 10 (the software is called "EMMA")
- Connect the mobile phone to the USB while pressing the volume down button (below) (the green LED lights up)
- EMMA now finds the cell phone
- select the current firmware and also the software (34.4.A.2.107.FR .....) and flash (I took version 107 ..., 118 probably works too)
1.3) Replace the firmware - Install TWRP on the mobile phone with "fastboot flash recovery /home/reinhard/Downloads/twrp-3.3.1-0-suzu.img" (download the file from the Internet)
- Start TWRP with (USB connector pulled + vol-down + power) and then in TWRP "Wipe" data + system + cache + dalvik cache
- then flash the following file with fastboot "fastboot flash oem /home/reinhard/Downloads/SW_binaries_for_Xperia_AOSP_N_MR1_5.7_r1_v08_loire.img" (Attention, unzip the zip file beforehand !!)
1.4) Install Ubuntu Touch - then bring cell phone in Fastboot mode = blue LED
- connect to the UBPort installer (manually) and have it installed (version ... devel; wipe data; ...)
- done (and me too)
What's not possible (as of May 16, 2018)
Everything works great (high praise to the "porter"), except for:
- camera: no flash; no zoom; no video
- LTE is not displayed, but still seems to work
- the battery lasts approx. 1 day (seems to be too small for the cell phone anyway)
- Bluetooth headset is not working
Alternatives
I had tested Sailfish-OS in advance, but I am disappointed:
- I find the operation and the look horrible
- the app store has practically nothing useful to offer (the open store from Ubuntu-Touch is much better)
- I also bought the Android extension for € 49, but it is only Android 4.4 - so it is no longer really usable