It does replace base game weddings but engaged sims can get married at City Hall.
The Sims 4 My Wedding Stories offers many different types and styles of weddings and pre-wedding celebrations for your Sims. If your Sims aren’t interested in a lot of fuss and planning surrounding their special day, or if the stress of planning a big elaborate wedding has gotten the best of them and they don’t want to deal with it anymore, they can elope at City Hall!
https://simscommunity.info/2022/02/23/the-sims-4-my-wedding-stories-getting-married-at-city-hall/