@mitch2 Yes, we do know. Fiber optic cables, lacking in any metal components, cannot transmit an electrical surge from point to point.
For this reason I use a fiber converter between the cable modem and Wifi router. There are still potential paths through the AC wiring, but that's dealt with by a UPS with surge protection.
The other place where Ethernet can pick up a surge is if the cabling is long. It acts as an antenna, and the longer the cable the higher a surge voltage can build up. Of course, whether this matters to you depends very much on where you live. First year I moved here we had several strong lightning storms which took out multiple neighbors cable modems, and a laptop of mine (via the power cord).