The Xperia phones are often horrendously locked down
Not really, at least when compared to most other brands. I’ve had three or four different Xperia models, and unlocked the bootloader on every one of them using official Sony tools. They even have official open-source software archives, which are very helpful to people who build de-googled “ROMs”.
The one thing that has been especially locked down is the TA partition, which contains DRM keys used for Sony’s proprietary apps. It’s not needed for an open-source OS like LineageOS.
For this phone specifically, it looks like official LineageOS support is already underway, despite it being a fairly new model:
I would definitely recommend a Pixel device if you’re going to go De-Googling.
Pixels do have unusually good support for user-installed OS, but the irony here is that you can’t truly de-google them, because no OS will change the fact that Google controls the hardware and firmware.