All the Sony Xperia phones consistently & eventually make it to LineageOS mainline (so LineageOS for microG support too), but these ROMs don’t tend to come until near then end of a device’s 2 year warranty. I would assume that this is when they get cheap/used enough that developers can get their hands on them. Sony provides all the tools to unlock so it isn’t difficult or locked behind some centralized server for unlock keys. However, the nice cameras the come with… well you need their proprietary app unfortunately or the camera becomes a plenty bad device with the default LineageOS software.
On the plus side you get to support the only brand still shipping flagships with microSD, a headphone jack, and the ability to unlock bootloader (bonus the the 5s are <6" screens which is rough to find smaller phones now). Google Pixels won’t get you a headphone jack or microSD & Asus Zenfones don’t have unlockable bootloaders.