Motherboard standoff screws are machine screws, so how do I fasten those to wood securely? Can I forgo standoffs entirely since wood isn't conductive?

Also, I'm looking at a spare Radeon RX 5600 right now and I can't find any holes that would make suitable mounting points (RX 7900 XTX is what I actually plan to mount).

I see an L-bracket under the PSU so at least that one looks straightforward at least.

Edit: It looks like that PCIe ribbon comes with a mounting bracket attached. Maybe that's how they did it here.