I found this from quick Googling https://forum-en.msi.com/index.php?threads/does-pro-z690-a-and-mag-z690-tomahawks-pcie-5-0-x16-slots-support-pcie-bifurcation.3

I found this from quick Googling https://forum-en.msi.com/index.php?threads/does-pro-z690-a-and-mag-z690-tomahawks-pcie-5-0-x16-slots-support-pcie-bifurcation.375664/ https://forum-en.msi.com/index.php?threads/does-pro-z690-a-a... Perhaps why they dropped the support is because the reason you wrote? Still I wonder is it possible to have Gen5 x8 and Gen3 x4/x4.