Congratulations on your upcoming wedding. We were in Mykonos and Santorini in May 2024. We did not visit any restaurants in Oia, so I don't have a recommendation for Oia. One recommendation is to visit a winery at sunset (Santos) is a good option, it is near Pyrgos. In the evening, you can book a table on the patio, sip very good wine, have a nice charcuterie platter and see the sun set without as many crowds. The other option is to watch the sunset from Franco's Cafe in Pyrgos. This is not a dinner place, it is very casual, but it has spectacular views. It is a bit of an upward hike up to Franco's, but Pyrgos is not as crowded and is a delightful town to visit.
However, for Mykonos, we enjoyed Nikolas Taverna https://www.nikolas-taverna.com/. It is a family run restaurant since 1967 with amazing seafood. If you go, book a table right on the beach at sunset, it is magical.
The other option for a WOW experience is 180 Sunset Bar: https://180.bar/. It is a panoramic view above the town of Mykonos with spectacular views at sunset. The food is good, not spectacular. You are really going there for drinks and the view. There are multiple seating options, depending upon your budget, so take a look at the 360 degree views from the website. Plan to stay the entire evening as they have really good entertainment, plenty of places to take pictures.
Have a great trip.