This may sound dumb or be helpful so I’ll toss it in just in case:

Depending on when they’re built, a lot of houses’ RJ-11 phone jacks are actually using CAT-5E. If you’re lucky, they’re individual runs and not daisy-chained!

The way they set up the runs here is weird though, they’re cat-5E but we have no fancy junction box. It all runs to some hatch on the side of the house presumably for telecom/satellite TV installers.

So it was cool finding out there’s already capable infrastructure in the walls, but you gotta replace the wall jacks with RJ-45 and then the next trick is figuring out a switch that can handle a garage that could get to 100ºF + in summer…