It's not so much about motherboard brand as it is about the chips used on any given model. For example, ASUS makes some boards with Intel i225-v ethernet, and others with Realtek RTL822x ethernet. The Intel chip is notorious for stability problems on all platforms, and although I think the linux drivers eventually managed to work around them, the boards with the Realtek chip avoided those problems entirely.

With that in mind, I suggest you look at a few key chips used on any board you're considering, and search linux forums for problem reports with their model numbers. In particular:

• Ethernet
• Wi-Fi
• Audio

Sometimes you can find comparison charts for such things, like this one for socket AM5 boards

Also, it's nice to have a board that can update its own BIOS from a flash drive, rather than requiring a Windows program to do it.

Use https://linux-hardware.org/ to check stuff. Ask questions with the links if you do not understand the reports. Everything you can build with has a proprietary bootloader, even the System76 stuff is proprietary.

Don't know about the drivers part.
But I was just looking into motherboards a bit, and it looks like the Asrock x870E Nova is a great bang for the buck.
Asrock in general seems to be overall better than the rest these days.

Check for WiFi and Bluetooth drivers compatibility first. Every x86_64 motherboard should work with Linux well, as in, it will boot and all USB/PCI Express/SATA ports will work. What you should care are peripherals soldered onto the motherboard, like WiFi, Bluetooth, extra Ethernet ports, ten years ago I would say soundcards but nowadays all integrated soundcards are supported, some motherboards have strange ports like Firewire which might not be supported, integrated videocards are now soldered directly onto CPU and not on motherboards like before so HDMI ports should all work on any motherboard.

And yes, as the other commenter said, check that firmware update does not require some Windows program, and could be done only with USB drive and selecting some option in the BIOS/UEFI menu.

I am not sure what makes a motherboard Linux-friendly... I guess fwupd integration with LVFS would be nice? Still, I am happy with my MSI B650 Tomahawk, since I can just put the latest firmware into an exFAT formatted thumb drive and update with it. All my laptops in the past had only supported firmware updates with Windows-only executables. I think I really should check out Framework for my next laptop.

Only potential issues I can forsee are audio driver and networking driver, but I highly doubt either of those will be an issue with any modern motherboard.

I would just buy whatever and install Linux on it. As for which one to buy, just get one from a reputable brand (Gigabyte, ASUS, ASRock, MSI, and whatever else I'm missing).

The CPU and the BIOS/UEFI/other primary bootloader are all that really matter from a software freedom perspective (hardware freedom is a different beast altogether that still has no truly viable solution for 100% freedom from head to toe yet), and unless you go with an old mobo supported by libreboot or canoeboot, then you're going to have to deal with having Intel ME or AMD PSP, which are segmented processors inside of the CPU that has full memory access and runs proprietary code along with having a proprietary BIOS.

Uhh someone can correct me if I'm wrong but I don't think the motherboard cares what os you use nor does it much (if any) impact on gaming performance. In fact, the only "Linux compatible" piece of hardware I would suggest is an amd GPU, although even that isn't really necessary anymore as several distros (PopOS, Nobara, and bazzite off the top of my head, probably more) have isos that come bundled with Nvidia drivers