A user in XDA Forums recently asked about instructions for installing LOS on Sony XZ Premium maple).fastboot.
These instructions apply equally to installing my unofficial builds of IodéOS which include zip files for flashing with recovery as well as for flashing with fastboot. They also apply to the other yoshino family devices XZ1 poplar and XZ1 Compact lilac
So here’s what I wrote
Please read though all the following instructions - including the linked sites - BEFORE YOU START TO MAKE ANY CHANGES
The process consists of the following steps
Follow the instructions on the Sony Open devices site for getting your unlock code and for unlocking the bootloader , which also cover installing the tools you will need on your computer, and checking that the bootloader can be unlocked on your device. (If devices were initially shipped ‘network locked’ - i.e. only working for a particular network operator - it will probably not be possible to unlock the bootloader, even after removing the network lock. If you are buying a second-user device, make sure it is ‘factory unlocked’ not just ‘networked unlocked’. If you are unsure, ask the seller to run the service menu as described on the Sony site )
Follow the LineageOS instructions for installing a custom recovery to flash the TWRP image linked in the first post in this thread , making sure you format your data partition as described there
Follow the LineageOS instructions to flash the ROM zip file using TWRP recovery
If you want to install GApps, follow the LineageOS instructions but using the version of GApps linked in the first post in this thread
Reboot
For steps 3 & 4, instead of using adb sideload as described in the LineageOS instructions, you can copy the ROM zip file and the GApps zip file to an SD card on your device and flash them using the TWRP install menu, making sure you format your data partition first.