To begin with, we have a General Computing section of this forum which would be better suited to your inquiry.
Halcyon is an Intel fanboy, don't take his word for it, he just hates AMD. /me licks Halcyon
While there will always be the exception to the rule, I've found that the vast majority of motherboard hardware out now has fairly good Linux support. If you think, there's not really much to not be supported. You have sound, which has near universal Linux support, even for stranger stuff, NICs which honestly tend to have better Linux support than Windows, USB controllers which almost always have drivers, and chipsets/CPUs, which are common, known parts. Definitely do AMD, they're at the price to performance and energy to performance top right now, and they have features, like PCIe 4 that Intel is still dreaming of. Avoid Intel unless you get good deals on older hardware. They're still on their 14nm stuff and will be for a while.
Budget and application are always the determining factors when building any machine. We don't know what you intend to do with your machine, if you care about graphics, RAM size or speeds, NVMe. In general any common motherboard from the likes of MSI, Gigabyte, ASUS, and ASRock will do fine. Brands like EVGA and BIOSTAR are also good choices, but I'm not even sure if they make new motherboards anymore.
Get the absolute newest chipset possible, the X570. While you may not need things like overclocking, you /will/ want better new CPU support, and PCIe 4, which will only come on boards with the X570.
Next suggestion is to get an NVMe SSD. Corsair makes good ones, Samsung is the gold standard, get a PCIe 4 one. Good, fast storage will make a lot of difference in a lot of places.
As for Linux version, if anything the LTS versions are less likely to have all the support you want, as they tend to be centered around older kernel versions. Use what you like, but if your chief concern is hardware support, rolling distributions which always have the newest kernel hot off the presses like Arch Linux are not bad ideas. That being said, you'll most likely be fine with the latest Ubuntu.