I spent a week in Hawaii in December of last year. Stayed on the western side of Oahu.
Its berkeleying gorgeous. Lots of cool E36 M3. Amazing sights, hikes, etc. I was only swimming in the ocean water for maybe 40 mins total our whole trip. Plenty of other stuff to do.
Get this book, its well worth the $20 just in the time it will save you planning activities: https://www.amazon.com/Oahu-Revealed-Ultimate-Honolulu-Waikiki/dp/1949678121/
Some of my favorite stuff was just unmarked trails and while you can find them all on google, that book puts it all in one place. The spitting cave is just a little tiny unmarked trail between two houses at the end of a cul-de-sac. The hike up to the "pink pillbox" is just a random trail next to the road into a subdivision.
If you want to be on a boat and out of the sun, the submarine tours that leave out of Waikiki are fun.
Pearl Harbor was something my family wanted to do. When we went there the docks were under repair so you couldn't go out to the Airzona. That honestly was just about the least exciting part of the trip.
Heed aircooled's warning about the traffic. It is bad. Like almost everywhere, almost all the time, not just Honolulu. A lot of the island is protected parks, or mountains with limited passages. The city has awful rush hour traffic, but even as far as you can get from it, you are on one lane roads and something as simple as a few people struggling to park at a roadside attraction can clog everything up pretty bad. I spent at least 3x more time in the car than I anticipated that trip.
On a related note to the above, youve likely heard of "island time". Its not as bad as it is on small islands, but there is definitely some of it going on. IIRC It took us like 7 hours to get from our flight to our rented villa like 15 miles away between the COVID check after landing, getting our luggage, waiting in line for the rental car check in, then waiting for the actual car, then sitting in traffic, then checkin in at the villas. Every step took way longer than I thought it would. Prepare for that.
A few random pics (that apparently google has compressed the berkeley out of... wow)
You've seen these mountains in just about every jungle movie ever (most notably, Jurassic Park/World)
Standing on a pillbox:
About to walk up a lot of stairs straight up @ koko crater: