The changelog for 23w18a says:

• Walking on the ocean floor will produce a step sound for the block you are walking on at a lower volume and pitch

However, there seems to be no change between 23w17a and 23w18a.

Steps to reproduce

1. Open Minecraft in both 23w17a and the latest snapshot
2. Place some blocks underwater with loud stepping sounds
3. Make sure Players sounds is at 100%
4. Walk over them and compare the volume and pitch of the sound in both versions