It's hard to avoid at least a little RGB in modern consumer motherboards.
I've been pleased with performance of my Asus B550m TUF Gaming Plus with a 5800X processor. While it is mATX it also has an ATX variant. The on-board RGB is minimal and you can easily and completely disable it in BIOS without any need to run a utility in the OS.
While the performance has been good, I do have a few beefs. One is, by default, it will try to download and install the Armoury Crate app. You have to disable that in BIOS to prevent it, do so because once installed it's almost impossible to completely remove all the services.
Another is the annoying way Asus differentiates product lines. The TUF is a mid-range so it doesn't get all the sensors the upper range Strix lines get, so it's missing a sensor to report VRM temperature and one also to report DDR4 DIMM Voltage.
Even for a 5800X the VRM is over-designed though so a temp sensor isn't really an issue as the VRM stays very cool whatever I'm doing. You can also monitor it with an IR thermometer easily enough. V-DIMM not being reported is annoying since you have to pretty much trust the voltage set to be right. I use some heavily overclocked Samsung B-die that needs pretty high voltage to stay stable, it would be nice to know it's not going over what I set.