It’ll be fine, it’s grounded through the PSU and the expansion cards anyway. Even if you were concerned, you could affix a ground strap between the chassis and one of the mounting holes.

paradigital wrote on 2022-07-02, 16:19:

It’ll be fine, it’s grounded through the PSU and the expansion cards anyway. Even if you were concerned, you could affix a ground strap between the chassis and one of the mounting holes.

That's precisely what I'd thought as well. Seems to be plenty of grounding opportunities but it was one of those questions I'd always been a little curious about.

Yes generally it is important to ground any motherboard or backplane to the chassis using the tinned type mount holes, those that are just holes in the board use nylon or plastic.
Why ? The board is designed a certain way that you want the grounds to be as near zero ohms as possible between other ground points. That is why boards have those tinned holes in specific places where specific components and capacitors have their grounds. Usually they all tie together thru traces but there could be some ohmage if going from the PSU ground to the farthest tinned mount point. The PSU ground and chassis ground are same the idea is to keep resistance on that ground plane as low as possible between points and relying on the cards to ground properly is not always a good thing as some adapters have a specific jumper to ground the mount to PSU ground thru the slot or chassis.
Sure you might get by without grounding them but it always best to ground them to chassis if possible so that there is not some board specific change in the ground plane.
Ok probably TMI and probably not so important but thought you should know there is a reason they tin certain mount holes on boards 😀 edit fixed a typo 🙁

Some of the old OEMs I have use plastic standoff and so those boards are grounded through the I/O shield

All the old IBM 5150/5160/5170 use plastic standoffs as well. When I was young and poor I built a PC case entirely out of wood. It will be fine.

See if there's any tapped holes lined up with any holes in the motherboard, and put a brass standoff in it. If it just seems to have square slot arrangements it might need those clip-in standoffs, but be careful that those don't take up too much room on the backside of an older board and short something near the hole because the top of them is bigger than the old brass standoffs.