That said, look at B650(E)/X670(E) boards for this, the X870 ones share lanes between the GPU slot and the second CPU-connected m.2. You don’t lose much, but there’s fewer ones with USB4 if that’s a concern. Also exterme memory overclock are more minuted on 6 series boards in general.
Asrock boards seem like a good pick, or asus proart if you need more connectivity.
B850s are mostly PCIe 5.0 x4 + 4.0 x4 from the CPU. B650 Steel Legend is too.
MSI does dual CPU 5.0 on the B850 Tomahawk, B850 Edge, and also X870 (non-E) Tomahawk with USB 4 PCIe bifurcation but for all three it’s pretty much either have a dGPU or adequately heatsink the third slot drive for 5.0 operation, not both. The X870Es I know offhand have similar limitations, though maybe there are some that get a 5.0 drive down to the fifth, six, or seventh slot where it’s heatsink it’ll clear a three slot dGPU. Easier if it’s an iGPU or two slot dGPU build.