m.2 can get hot, installing them under a hot video card cooler is a judgement call, especially if there is more space elsewhere. The truth is most people probably don't use their 1x slots.
I found some ultra low profile pcie extensions (basically mining risers that use a USB3 cable) that allow me to relocate the cards elsewhere but still install them in slots that are under big GPU fans.
As mentioned, there is a wide variety of these available of different types. They were made popular and available enough by the mining boom that there are different styles (and different qualities).
There are M.2 extension cables, I have one that lets me put the M.2 in to the drive bay away from the motherboard. There's also M.2 bifurcation cables. And you can also put the M.2 on PCIe cards, with or without a PLX switch.
I found some ultra low profile pcie extensions (basically mining risers that use a USB3 cable) that allow me to relocate the cards elsewhere but still install them in slots that are under big GPU fans.