
Sorry to hear about the notebook. It will not be easy to find the motherboard. Nothing you can do about a lightning strike. Quite often the components get fried.
The Ethernet port itself has galvanic isolation up to about 2kV. Ethernet surge tolerance was a hot topic and ITU had several recommendations and the last one was K.126 issued 2017 which describes hazards and possible methods of protection.
With lightning is nothing is predictable (other than it takes the shortest path to ground

) There are various kinds of isolators, but these are expensive. There are isolators that's packaged with Medical equipment that offers protection to 8kV. But these are mostly designed for human safety.
The only way to guarantee complete isolation is possibly to use two media converters back to back. (Ethernet to Fiber and back). Then there is total optical isolation of the Ethernet port.