Same as on all my other machines: Gentoo. 
I copied /etc and /var/lib/portage/world off my old Dell Latitude 7370 (the machine this one is replacing), booted a temporary Lubuntu 21.10 system off an ISO on an SD card, and installed things more or less as usual.
This page suggests that a newer kernel than you might normally run would be a good idea, so I have sys-kernel/gentoo-sources ~* in /etc/portage/package.accept_keywords.
I had some trouble at first getting WiFi working, but that was misconfiguration on my part between NetworkManager and iwd. Specifically, /etc/NetworkManager/conf.d/iwd.conf should contain the following:
[device]
wifi.backend=iwd
wifi.iwd.autoconnect=yes
Also, iwd needs to run in the default group: rc-update add iwd default. I think I might’ve forgotten some of this stuff when I switched the old machine from wpa-supplicant to iwd.
Before figuring that out, I cribbed the kernel configuration (running 5.15.8) from Lubuntu, since WiFi was working there. I might try reverting reverted to Gentoo’s stock kernel config…it probably works, too, and would be less hassle to get going…
I only got the computer this past Monday, and have only had evenings to tinker around with it thus far. I got my usual KDE setup running last night shortly after getting WiFi working. The only annoyance I’ve run into so far is a lack of tap-to-click on the touchpad. After a bit of poking around, I found the touchpad controls in KDE system settings to enable tap-to-click. w00t!