The law says that copy is something that is "fixed" on a tangible medium. DRAM might not fall under that definition.

It does if the copy is "more than transitory". Software in RAM is a full copy and remains there as long as the program runs, so that can be an unlicensed copy per MAI v Peak (but if you had a license to the original, there's an explicit legal carveout for RAM copies). It would depend on how far the data is buffered and how long it is cached.

Yes, and that's why running an executable can technically be copyright infringement. This came up in some anticheat lawsuits.

Which is an absurd position. It's not far removed from sayng that reading something and committing it to memory is an act of copying.