Device brand : Sony
Supported Android versions : Nougat, Oreo, Pie (?) including Sony AOSP
Custom rom supported :
LineageOS 14.1 and 15.1 : unofficial and not maintained
Others : https://forum.xda-developers.com/xperia-x/development
OmniROM 8.1 : official and not maintained
Sony AOSP 7.1.2, 8.1 : official and partially maintained
So far, I would recommend porting /e/ for this device to Oreo as Sony AOSP 8.1, OmniROM 8.1 and unofficial LineageOS 15.1 versions are already available.