I’ve always connected the two Macs via Ethernet cables to one router, and never had a hardware problem.
The software, however, was another thing… every time I tried to use Migration Assistant, it failed to work, and in fact made an awful mess. Perhaps because I wait so long between migrations? Or because my systems are all so heavily customized? I don’t know. I’m aware that Migration Assistant works fine for many people, but I’ve given up on it.
A few articles that might help:
- How to migrate to a new Mac
- If macOS’s Migration Assistant fails…
- Step-by-Step Guide to Manual Mac System Migration
(That last is a very old article, but still somewhat helpful perhaps.)
Good luck.
P.S. Speaking of things not working right… why do the three links I created (above) look gigantic in my browser, compared to all the other text? Do they look like that to everyone?
[I’ve fixed them; they were prefixed with #, which equates to H1, rather than *, which creates a bullet list. -Adam]