You can get a PCIe X1 riser cable to move it to somewhere else, although that's only useful for cards that don't have any external ports, and if your case has somewhere else to mount it - for example, if you're using a microATX board in a full size case and you've got a few otherwise useless empty brackets at the bottom. Otherwise, no, you simply can't use the slot if a card won't physically fit in it due to another card.

I have a hard time telling from the videos, not sure if I'm seeing right, but in this one, it looks the whole mass of the sound card may be facing downwards where there is space. Unfortunate placing of the slot, will restrict cooling a bit in case it does fit.

The massive CPU cooler I have is also a weird one where fan is blowing towards the GPU, but it's not as tight and never had overheating problems. Not the most optimal, but still, the computer keeps humming along.

I would get a PCI sound card from a used market. I don't know if there was a reason for it, but sound cards would usually go to the very bottom slot. Unless you have problems like interference from the video signals or mouse, it won't directly improve quality, and might not like sitting so close to the video card. A professional soundcard gives more options for I/O and an accurate signal path for recording. Maybe less bloated drivers or stability.

The slots give you options to use either a big video card or another card. Maybe a small network adapter would fit. cards always have the "mass" on the bottom.

There's another PCIe x1 slot that's obstructed by the graphics card, so the device in the second slot would still be one slot apart, at least connection wise.

It does fit. No apparent problems with sound, graphics card's temperature remains normal under load. I'm not sure if there's a difference from before as I don't recall the exact number, it was around 45 ℃ under load and it's still in that range. The case does have 400 mm side fan.

You don't need a lot of space, will it look odd yes but all that matters is if the temp is good.

One of the main selling point of my motherboard was the one PCI-e 1x slots were above the 16x slot so I could add a sound card without getting in the way of the GPU fan.

It seems most other, pricier flavors of Asus M3N78 have PCIe 1x above PCIe 16x slot. I was going for a totally different motherboard from Gigabyte, don't recall the model, but something went wrong with stock where I was buying and this one was readily available and teenage me wanted a new computer ASAP. A bit ironic considering the time I spent researching components I wanted.