Does OS X support SMB Direct (RDMA)?
Well, got this from ATTO tech support today:

macOS (macOS 10.14.x, macOS 10.15.x Catalina, &amp; macOS 11.x Big Sur)
does not support SMB Direct, nor RoCE.

:-(
I sent a feature request to Apple. I'm sure that because I said so they'll get right to it.