I’ve never dwelled on how the mechanics of galactic travel. Stories like to imagine many things but I don’t expect such travel will ever be possible. Mostly I don’t find the prospect of FTL travel at all intriguing. Why should great distances be necessary to encounter a mystery to confound our understanding?
This is sort of why I lean towards universalism. If there is any probability of intelligent beings out there, then either the bible plays out on every “Earth,” or we’re silly to think that we are special enough to be chosen out of the entire galaxy.
One system I read of made nearly-instantaneous FTL possible, but it required gates in reasonably flat space that are “tuned” the same. This meant that to initially get to another star sublight was needed, and the best velocity the folks in the stories had was 0.8c. It also meant that once the jump between gates was made getting from the gate to the destination planet took months since gates had to be fairly far out in a stellar system.