The hour either side of six is the worst weekday window on the causeways in both directions, and sunset falls inside it for roughly half the year.
Westbound at sunset is the bad one. You are travelling into the commuter flow towards the mainland and directly into the glare, on a road with drawbridge sections and no alternative. The MacArthur runs twelve to fifteen minutes mid-morning and forty to fifty in that window, with rideshare surge stacked on top.
So: book your sunset on the side you are already on. This is one of the few pieces of advice on this site that costs nothing to follow. Every side of the bay has a good option, and the table further up this page says which direction to face from each.
If you must cross for dinner, cross after eight, once the light has gone and the peak with it. Sunset first, then the crossing, then the table — never the other way round.
On the island specifically, the free trolleys are the sensible way to reach the bay side at six: fifteen to twenty minute headways, no parking to find, and no surge. On the mainland, the free Metromover puts you on the downtown waterfront without a car at all.
One weekend note. On a Sunday afternoon the reverse flow builds from about three as day-trippers return, and the beach car parks empty into the same two causeways at once. A Sunday sunset is best planned from wherever you already are, with no driving in it at all.