I'm not much of a Linux user, but I've been trying elementary OS 0.4.1 Loki via Parallels and like it a lot. Unfortunately elementary OS 5 Juno has been buggy for me (random black screens requiring a reboot), so I'm stuck on Loki for now.
I was tempted to put elementary OS on my 32-bit 2006 MacBook (the one that currently has Windows 10), but there isn't a 32-bit version of elementary OS anymore.
I'm pretty pleased with the X1E: it's not quite MBP-level thin, but it's still a great balance of power and portability. NotebookCheck has a review that's worth checking out.
elementary OS feels fast, familiar, and refined. It's not quite as fleshed out as other distros like Mint (or macOS itself, for that matter), but it's getting better with each release.
The 4K HiDPI screen on the X1E is vibrant. My biggest concern was that the HiDPI scaling on Linux wouldn't be up to snuff, but I've been pleasantly surprised. The scaling for GTK apps was perfect right out of the box. There were some extra steps to get Qt apps to scale properly and inherit the GTK theme, but they look great now. Wine and Steam basically just required checking a box to get the scaling to work.
Happy to answer any specific questions you have.