I dual boot OpenBSD on it, and it's been doing fine. The out of the box experience is pretty bare although the default window manager cwm is surprisingly nice once you get to know it. Note that apmd, the power management daemon used to manage CPU speed and low-battery suspend, is not enabled by default. The high-DPI screen required some adjustments in Xresources (I haven't dared try a multi-monitor, mixed DPI setup).

NetBSD seemed okay to but I've only used it a little bit. It actually set up X pretty well for the screen using some built in script with heuristics to determine font size from the screen metrics.

There's been a bunch of progress on FreeBSD, and OpenBSD isn't that much worse

No wifi driver for Framework 16. Was fun installing (and surprisingly quick) and playing around a little. But unfortunately that's a dealbreaker for me.

Power management, webcam, trackpad, accessories, etc tend not to be a good fit for niche BSD and Linux. Stick to desktop or server.