There's not a lot, honestly. Pretty much all discrete motherboards are gaming rigs of some form. The basic computer for general users is now a "laptop" (which tend to work quite well for general gaming, FWIW). But the low end choices from the regular suspects (Gigabyte, MSI, Asus) are generally fine in my experience. You do occasionally get a weird/flawed device, like you do with many product areas.
Yeah it really seems the market has bifurcated into "DIY build-a-computer" targeted towards gamers, bedazzled with RGB and all that jazz, and "Buy a used/refurb Dell mini-atx office desktop computer", assuming they don't just default to 'buy a laptop' as you point out.
