I think you’ll find the slightly older hardware tends to be better supported. A laptop that is 2 - 3 + years old will have most of the QubesOS issues either ironed out or at the least will have been discussed. When you’re going with new hardware, you’ve got to be comfortable with a bit of a risk of not everything working 100% on day #1, but at time rolls on, it gets better.
The HCL is a really good starting point, but you want to combine it with other sources of information as well. So perhaps make a shortlist of a few models that you’re looking at, check the HCL and then check these forums and the Qubes Issues Github section. Also, pick out the CPU that you’re going with and run that through a search separately and see how it stacks up.
Also, make use of some of specific sub-redddits. In the case of the Thinkpads, you’ll want to check sub-reddits for Lenovo, Thinkpad, QubesOS and even find and check general Linux compatibility for the hardware you’re getting.
I recently went through the process and went with a P1G4. Overall I’m happy, but there’s a few things which I still need to work through and investigate. There’s a thread on here with my notes from it.
The X13 (Gen2) is nice and I was closely looking at it, but for me personally, I wanted more RAM (64GB) and TB4.0 support (docking and driving lots of monitors is important for me). No idea about the 5G WWAN sorry. At a guess, I imagine it would present itself as a PCI device similar to onboard Wired/WLAN NICs so it’s just a matter of assigning it to “sys-net” and then as long as the underlying Linux OS for sys-net (Fedora34 or Debian11) supports it, you’re good to go. But you’ll have to check, I’m only guessing here.
The Librem 14 is nice and I really love the hardware switches and onboard NIC. But it was using 10th Gen Intel Processors (I needed 11th gen for TB 4.0 + 8 cores).
Another one I had on my list was the Tongfang PF4NU1F (sounds dodgy, I know; but the specs were good, especially for sustained CPU load on an AMD Octacore). This model is the OEM for Tuxedo Pulse and KDE Slimbooks.
A final thing, if you’re looking at ultra-portable style laptops with lots of cores and compute ability (especially Intel Octacore) make sure you research and read up on any potential thermal throttling issues due to poor heat-dissipation.
Hope that helps.