Based on my experience this is normal. Even AAA games have a peak on launching day, and the following days it gets more quiet (in comparison).
Every time you post something on social media, depending on your audience, you will get a similar spike. If you don’t post anything, the only people looking at your game will be ones that found it randomly upon searching on Itch.
Once the game is in a stable version, and you make a “Major Update” on Itch, it will bump your project in the game list and you will (most likely) get a similar peak.